Method and apparatus for determining an inherited affine parameter from an affine model

ABSTRACT

An apparatus for video decoding includes processing circuitry. The circuitry can be configured to receive a current block that is affine coded and included in a current coding tree unit (CTU), and determine an inherited affine candidate based on regular motion information of two minimum blocks in a rightmost column of minimum blocks of a left neighboring CTU of the current CTU when the current block is adjacent to a left boundary of the current CTU.

INCORPORATION BY REFERENCE

This present application is a continuation of U.S. application Ser. No.16/750,862 filed Jan. 23, 2020, which claims the benefit of priority toU.S. Provisional Application No. 62/797,892, “Affine Model Inheritancewith Reduced Local Buffer Requirement” filed on Jan. 28, 2019. Theentire contents of each of the aforementioned applications areincorporated by reference herein in their entirety.

TECHNICAL FIELD

The present disclosure describes embodiments generally related to videocoding.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent the work is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Video coding and decoding can be performed using inter-pictureprediction with motion compensation. Uncompressed digital video caninclude a series of pictures, each picture having a spatial dimensionof, for example, 1920×1080 luminance samples and associated chrominancesamples. The series of pictures can have a fixed or variable picturerate (informally also known as frame rate), of, for example 60 picturesper second or 60 Hz. Uncompressed video has significant bitraterequirements. For example, 1080p60 4:2:0 video at 8 bit per sample(1920×1080 luminance sample resolution at 60 Hz frame rate) requiresclose to 1.5 Gbit/s bandwidth. An hour of such video requires more than600 GBytes of storage space.

One purpose of video coding and decoding can be the reduction ofredundancy in the input video signal, through compression. Compressioncan help reduce the aforementioned bandwidth or storage spacerequirements, in some cases by two orders of magnitude or more. Bothlossless and lossy compression, as well as a combination thereof can beemployed. Lossless compression refers to techniques where an exact copyof the original signal can be reconstructed from the compressed originalsignal. When using lossy compression, the reconstructed signal may notbe identical to the original signal, but the distortion between originaland reconstructed signals is small enough to make the reconstructedsignal useful for the intended application. In the case of video, lossycompression is widely employed. The amount of distortion tolerateddepends on the application; for example, users of certain consumerstreaming applications may tolerate higher distortion than users oftelevision distribution applications. The compression ratio achievablecan reflect that: higher allowable/tolerable distortion can yield highercompression ratios.

Motion compensation can be a lossy compression technique and can relateto techniques where a block of sample data from a previouslyreconstructed picture or part thereof (reference picture), after beingspatially shifted in a direction indicated by a motion vector (MVhenceforth), is used for the prediction of a newly reconstructed pictureor picture part. In some cases, the reference picture can be the same asthe picture currently under reconstruction. MVs can have two dimensionsX and Y, or three dimensions, the third being an indication of thereference picture in use (the latter, indirectly, can be a timedimension).

In some video compression techniques, an MV applicable to a certain areaof sample data can be predicted from other MVs, for example from thoserelated to another area of sample data spatially adjacent to the areaunder reconstruction, and preceding that MV in decoding order. Doing socan substantially reduce the amount of data required for coding the MV,thereby removing redundancy and increasing compression. MV predictioncan work effectively, for example, because when coding an input videosignal derived from a camera (known as natural video) there is astatistical likelihood that areas larger than the area to which a singleMV is applicable move in a similar direction and, therefore, can in somecases be predicted using a similar motion vector derived from MVs ofneighboring area. That results in the MV found for a given area to besimilar or the same as the MV predicted from the surrounding MVs, andthat in turn can be represented, after entropy coding, in a smallernumber of bits than what would be used if coding the MV directly. Insome cases, MV prediction can be an example of lossless compression of asignal (namely: the MVs) derived from the original signal (namely: thesample stream). In other cases, MV prediction itself can be lossy, forexample because of rounding errors when calculating a predictor fromseveral surrounding MVs.

Various MV prediction mechanisms are described in H.265/HEVC (ITU-T Rec.H.265, “High Efficiency Video Coding”, December 2016). Out of the manyMV prediction mechanisms that H.265 offers, described here is atechnique henceforth referred to as “spatial merge”.

Referring to FIG. 1, a current block (101) comprises samples that havebeen found by the encoder during the motion search process to bepredictable from a previous block of the same size that has beenspatially shifted. Instead of coding that MV directly, the MV can bederived from metadata associated with one or more reference pictures,for example from the most recent (in decoding order) reference picture,using the MV associated with either one of five surrounding samples,denoted A0, A1, and B0, B1, B2 (102 through 106, respectively). InH.265, the MV prediction can use predictors from the same referencepicture that the neighboring block is using.

SUMMARY

Aspects of the disclosure provide methods and apparatuses for videoencoding/decoding. In some examples, an apparatus for video decodingincludes processing circuitry. The circuitry can be configured toreceive a current block that is affine coded and included in a currentcoding tree unit (CTU), and determine a first inherited affine candidatebased on first regular motion information of two first minimum blocks ina rightmost column of minimum blocks of a left neighboring CTU of thecurrent CTU when the current block is adjacent to a left boundary of thecurrent CTU.

In an example, the circuitry is further configured to determine controlpoint motion vectors (CPMVs) of the current block based on an affinemodel determined based on the first regular motion information of thetwo first minimum blocks. In an example, the circuitry is furtherconfigured to determine sub-block motion vectors (MVs) of the currentblock based on the first regular motion information of the two firstminimum blocks without deriving the current block's CPMVs.

In an example, the circuitry is further configured to determine thefirst inherited affine candidate based on a four parameter affine modeldetermined by using MVs of the two first minimum blocks that areadjacent to control points of an affine coded left neighboring block ofthe current block as an approximation of CPMVs at the control points ofthe affine coded left neighboring block.

In an example, the circuitry is further configured to determine thefirst inherited affine candidate based on a four parameter affine modeldetermined by using precise positions of two MVs of the two firstminimum blocks that are within an affine coded left neighboring block ofthe current block. In an example, a distance between the precisepositions of the two MVs of the two first minimum blocks is a power oftwo. In an example, a first one of the two first minimum blocks isadjacent to a control point of the affine coded left neighboring block,and a distance between the precise positions of the two MVs of the twofirst minimum blocks is a half of a height of the affine coded leftneighboring block.

In an example, the circuitry is further configured to include aninherited affine candidate from a history-based motion vector prediction(HMVP) table in a merge candidate list or an advanced motion vectorprediction (AMVP) candidate list that includes at most two inheritedaffine candidates.

In an example, the circuitry is further configured to determine a secondinherited affine candidate based on second regular motion information oftwo second minimum blocks in a bottom row of minimum blocks above a CTUrow including the current CTU when the current block is adjacent to thetop boundary of the current CTU.

In an example, the circuitry is further configured to determine thesecond inherited affine candidate based on a four parameter affine modeldetermined by using precise positions of two MVs of the two secondminimum blocks that are within an affine coded top neighboring block ofthe current block. In an example, a distance between the precisepositions of the two MVs of the two second minimum blocks is a power oftwo. In an example, a first one of the two second minimum blocks isadjacent to a control point of the affine coded top neighboring block,and a distance between the precise positions of the two MVs of the twosecond minimum blocks is a half of a width of the affine coded topneighboring block.

In an example, the circuitry is further configured to include aninherited affine candidate from an HMVP table in a merge candidate listor an advanced motion vector prediction (AMVP) candidate list thatincludes at most two inherited affine candidates when the current blockis adjacent to the top boundary of the current CTU,

In an example, the circuitry is further configured to, when the currentblock is not adjacent to the left or a top boundary of the current CTU,determine an inherited affine candidate based on an affine model of aspatial neighbor of the current block that is stored in a local buffer.

In an example, the circuitry is further configured to, when the currentblock is adjacent to a top-left corner, the left boundary, or a topboundary of the current CTU, check availability of affine coded blocksthat are outside the current CTU and neighbor the current block atpredefined candidate positions according to a predefined order, anddetermine one or more inherited affine candidates based on regularmotion information of minimum blocks corresponding to first N availableaffine coded blocks, N being an integer greater than zero.

In an example, the circuitry is further configured to construct a mergecandidate list or an AMVP candidate list, of which a maximum number ofinherited affine candidates is more than two. In an example, when thecurrent block is adjacent to a top or the left boundary of the currentCTU but not adjacent to a top-left corner of the current CTU, the mergecandidate list or the AMVP candidate list includes at least oneup to M1inherited affine candidates from an HMVP table, M1 being an integergreater than or equal to 2, and up to N1 inherited affine candidatesdetermined based on regular motion information of minimum blocks alongthe top or left boundary of the current CTU, N1 being an integer greaterthan or equal to 1. When the current block is adjacent to the top-leftcorner of the current CTU, the merge candidate list or the AMVPcandidate list includes at least two up to M2 inherited affinecandidates from the HMVP table, M2 being an integer greater than orequal to 1, up to K inherited affine candidates determined based onregular motion information of minimum blocks along the top and leftboundaries boundary of the current CTU, K being an integer greater thanor equal to 1, respectively, and at least one inherited affine candidatefrom an HMVP table and up to N2 inherited affine candidates determinedbased on regular motion information of minimum blocks along the leftboundary of the current CTU, N2 being an integer greater than or equalto 1.

In an example, the circuitry is further configured to construct a mergecandidate list or an AMVP candidate list including an inherited affinecandidate from an HMVP table that includes an HMVP candidaterepresenting an affine model with affine parameters.

Aspects of the disclosure also provide a non-transitorycomputer-readable medium storing instructions which when executed by acomputer for video decoding cause the computer to perform the method forvideo decoding.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, the nature, and various advantages of the disclosedsubject matter will be more apparent from the following detaileddescription and the accompanying drawings in which:

FIG. 1 is a schematic illustration of a current block and itssurrounding spatial merge candidates in one example.

FIG. 2 is a schematic illustration of a simplified block diagram of acommunication system in accordance with an embodiment.

FIG. 3 is a schematic illustration of a simplified block diagram of acommunication system in accordance with an embodiment.

FIG. 4 is a schematic illustration of a simplified block diagram of adecoder in accordance with an embodiment.

FIG. 5 is a schematic illustration of a simplified block diagram of anencoder in accordance with an embodiment.

FIG. 6 shows a block diagram of an encoder in accordance with anotherembodiment.

FIG. 7 shows a block diagram of a decoder in accordance with anotherembodiment.

FIG. 8 is a schematic illustration of merge candidate positions of amerge mode in accordance with an embodiment.

FIG. 9 is a schematic illustration of spatial neighboring blocks andtemporal neighboring blocks for a current block in accordance with anembodiment.

FIG. 10A is a schematic illustration of spatial neighboring blocks thatcan be used to determine predicting motion information for a currentblock using a sub-block based temporal motion vector prediction methodbased on motion information of the spatial neighboring blocks inaccordance with one embodiment.

FIG. 10B is a schematic illustration of a selected spatial neighboringblock for a sub-block based temporal motion vector prediction method inaccordance with one embodiment.

FIG. 11A is a flow chart outlining a process of constructing andupdating a list of motion information candidates using a history basedmotion vector prediction method in accordance with one embodiment.

FIG. 11B is a schematic illustration of updating the list of motioninformation candidates using the history based motion vector predictionmethod in accordance with one embodiment.

FIG. 12 is a schematic illustration of determining starting points attwo reference pictures associated with two reference picture lists basedon motion vectors of a merge candidate in a merge with motion vectordifference (MMVD) mode in accordance with an embodiment.

FIG. 13 is a schematic illustration of predetermined points surroundingtwo starting points that are to be evaluated in the MMVD mode inaccordance with an embodiment.

FIG. 14 shows a current coding tree unit (CTU) row and an above CTU rowon top of the current CTU row.

FIG. 15 shows an example of affine inheritance from an above CTU linebuffer.

FIG. 16 shows an example of affine inheritance from a left neighboringCTU.

FIG. 17 shows a current block adjacent to a top CTU boundary.

FIG. 18 shows a current block adjacent to a left CTU boundary.

FIG. 19 shows neighboring positions of a current block for availabilitychecking for affine coded blocks.

FIG. 20 shows a flow chart outlining a process according to someembodiments of the disclosure.

FIG. 21 is a schematic illustration of a computer system in accordancewith an embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

I. Video Coding Encoder and Decoder

FIG. 2 illustrates a simplified block diagram of a communication system(200) according to an embodiment of the present disclosure. Thecommunication system (200) includes a plurality of terminal devices thatcan communicate with each other, via, for example, a network (250). Forexample, the communication system (200) includes a first pair ofterminal devices (210) and (220) interconnected via the network (250).In the FIG. 2 example, the first pair of terminal devices (210) and(220) performs unidirectional transmission of data. For example, theterminal device (210) may code video data (e.g., a stream of videopictures that are captured by the terminal device (210)) fortransmission to the other terminal device (220) via the network (250).The encoded video data can be transmitted in the form of one or morecoded video bitstreams. The terminal device (220) may receive the codedvideo data from the network (250), decode the coded video data torecover the video pictures and display video pictures according to therecovered video data. Unidirectional data transmission may be common inmedia serving applications and the like.

In another example, the communication system (200) includes a secondpair of terminal devices (230) and (240) that performs bidirectionaltransmission of coded video data that may occur, for example, duringvideoconferencing. For bidirectional transmission of data, in anexample, each terminal device of the terminal devices (230) and (240)may code video data (e.g., a stream of video pictures that are capturedby the terminal device) for transmission to the other terminal device ofthe terminal devices (230) and (240) via the network (250). Eachterminal device of the terminal devices (230) and (240) also may receivethe coded video data transmitted by the other terminal device of theterminal devices (230) and (240), and may decode the coded video data torecover the video pictures and may display video pictures at anaccessible display device according to the recovered video data.

In the FIG. 2 example, the terminal devices (210), (220), (230) and(240) may be illustrated as servers, personal computers and smart phonesbut the principles of the present disclosure may be not so limited.Embodiments of the present disclosure find application with laptopcomputers, tablet computers, media players and/or dedicated videoconferencing equipment. The network (250) represents any number ofnetworks that convey coded video data among the terminal devices (210),(220), (230) and (240), including for example wireline (wired) and/orwireless communication networks. The communication network (250) mayexchange data in circuit-switched and/or packet-switched channels.Representative networks include telecommunications networks, local areanetworks, wide area networks and/or the Internet. For the purposes ofthe present discussion, the architecture and topology of the network(250) may be immaterial to the operation of the present disclosureunless explained herein below.

FIG. 3 illustrates, as an example for an application for the disclosedsubject matter, the placement of a video encoder and a video decoder ina streaming environment. The disclosed subject matter can be equallyapplicable to other video enabled applications, including, for example,video conferencing, digital TV, storing of compressed video on digitalmedia including CD, DVD, memory stick and the like, and so on.

A streaming system may include a capture subsystem (313), that caninclude a video source (301), for example a digital camera, creating forexample a stream of video pictures (302) that are uncompressed. In anexample, the stream of video pictures (302) includes samples that aretaken by the digital camera. The stream of video pictures (302),depicted as a bold line to emphasize a high data volume when compared toencoded video data (304) (or coded video bitstreams), can be processedby an electronic device (320) that includes a video encoder (303)coupled to the video source (301). The video encoder (303) can includehardware, software, or a combination thereof to enable or implementaspects of the disclosed subject matter as described in more detailbelow. The encoded video data (304) (or encoded video bitstream (304)),depicted as a thin line to emphasize the lower data volume when comparedto the stream of video pictures (302), can be stored on a streamingserver (305) for future use. One or more streaming client subsystems,such as client subsystems (306) and (308) in FIG. 3 can access thestreaming server (305) to retrieve copies (307) and (309) of the encodedvideo data (304). A client subsystem (306) can include a video decoder(310), for example, in an electronic device (330). The video decoder(310) decodes the incoming copy (307) of the encoded video data andcreates an outgoing stream of video pictures (311) that can be renderedon a display (312)(e.g., display screen) or other rendering device (notdepicted). In some streaming systems, the encoded video data (304),(307), and (309) (e.g., video bitstreams) can be encoded according tocertain video coding/compression standards. Examples of those standardsinclude ITU-T Recommendation H.265. In an example, a video codingstandard under development is informally known as Versatile Video Coding(VVC). The disclosed subject matter may be used in the context of VVC.

It is noted that the electronic devices (320) and (330) can includeother components (not shown). For example, the electronic device (320)can include a video decoder (not shown) and the electronic device (330)can include a video encoder (not shown) as well.

FIG. 4 shows a block diagram of a video decoder (410) according to anembodiment of the present disclosure. The video decoder (410) can beincluded in an electronic device (430). The electronic device (430) caninclude a receiver (431) (e.g., receiving circuitry). The video decoder(410) can be used in the place of the video decoder (310) in the FIG. 3example.

The receiver (431) may receive one or more coded video sequences to bedecoded by the video decoder (410); in the same or another embodiment,one coded video sequence at a time, where the decoding of each codedvideo sequence is independent from other coded video sequences. Thecoded video sequence may be received from a channel (401), which may bea hardware/software link to a storage device which stores the encodedvideo data. The receiver (431) may receive the encoded video data withother data, for example, coded audio data and/or ancillary data streams,that may be forwarded to their respective using entities (not depicted).The receiver (431) may separate the coded video sequence from the otherdata. To combat network jitter, a buffer memory (415) may be coupled inbetween the receiver (431) and an entropy decoder/parser (420) (“parser(420)” henceforth). In certain applications, the buffer memory (415) ispart of the video decoder (410). In others, it can be outside of thevideo decoder (410) (not depicted). In still others, there can be abuffer memory (not depicted) outside of the video decoder (410), forexample to combat network jitter, and in addition another buffer memory(415) inside the video decoder (410), for example to handle playouttiming. When the receiver (431) is receiving data from a store/forwarddevice of sufficient bandwidth and controllability, or from anisosynchronous network, the buffer memory (415) may not be needed, orcan be small. For use on best effort packet networks such as theInternet, the buffer memory (415) may be required, can be comparativelylarge and can be advantageously of adaptive size, and may at leastpartially be implemented in an operating system or similar elements (notdepicted) outside of the video decoder (410).

The video decoder (410) may include the parser (420) to reconstructsymbols (421) from the coded video sequence. Categories of those symbolsinclude information used to manage operation of the video decoder (410),and potentially information to control a rendering device such as arender device (412)(e.g., a display screen) that is not an integral partof the electronic device (430) but can be coupled to the electronicdevice (430), as was shown in FIG. 4. The control information for therendering device(s) may be in the form of Supplemental EnhancementInformation (SEI messages) or Video Usability Information (VUI)parameter set fragments (not depicted). The parser (420) mayparse/entropy-decode the coded video sequence that is received. Thecoding of the coded video sequence can be in accordance with a videocoding technology or standard, and can follow various principles,including variable length coding, Huffman coding, arithmetic coding withor without context sensitivity, and so forth. The parser (420) mayextract from the coded video sequence, a set of subgroup parameters forat least one of the subgroups of pixels in the video decoder, based uponat least one parameter corresponding to the group. Subgroups can includeGroups of Pictures (GOPs), pictures, tiles, slices, macroblocks, CodingUnits (CUs), blocks, Transform Units (TUs), Prediction Units (PUs) andso forth. The parser (420) may also extract from the coded videosequence information such as transform coefficients, quantizer parametervalues, motion vectors, and so forth.

The parser (420) may perform an entropy decoding/parsing operation onthe video sequence received from the buffer memory (415), so as tocreate symbols (421).

Reconstruction of the symbols (421) can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how, can be controlled by the subgroupcontrol information that was parsed from the coded video sequence by theparser (420). The flow of such subgroup control information between theparser (420) and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, the video decoder (410)can be conceptually subdivided into a number of functional units asdescribed below. In a practical implementation operating undercommercial constraints, many of these units interact closely with eachother and can, at least partly, be integrated into each other. However,for the purpose of describing the disclosed subject matter, theconceptual subdivision into the functional units below is appropriate.

A first unit is the scaler/inverse transform unit (451). Thescaler/inverse transform unit (451) receives a quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) (421) from the parser (420). The scaler/inversetransform unit (451) can output blocks comprising sample values, thatcan be input into aggregator (455).

In some cases, the output samples of the scaler/inverse transform (451)can pertain to an intra coded block; that is: a block that is not usingpredictive information from previously reconstructed pictures, but canuse predictive information from previously reconstructed parts of thecurrent picture. Such predictive information can be provided by an intrapicture prediction unit (452). In some cases, the intra pictureprediction unit (452) generates a block of the same size and shape ofthe block under reconstruction, using surrounding already reconstructedinformation fetched from the current picture buffer (458). The currentpicture buffer (458) buffers, for example, partly reconstructed currentpicture and/or fully reconstructed current picture. The aggregator(455), in some cases, adds, on a per sample basis, the predictioninformation the intra prediction unit (452) has generated to the outputsample information as provided by the scaler/inverse transform unit(451).

In other cases, the output samples of the scaler/inverse transform unit(451) can pertain to an inter coded, and potentially motion compensatedblock. In such a case, a motion compensation prediction unit (453) canaccess reference picture memory (457) to fetch samples used forprediction. After motion compensating the fetched samples in accordancewith the symbols (421) pertaining to the block, these samples can beadded by the aggregator (455) to the output of the scaler/inversetransform unit (451) (in this case called the residual samples orresidual signal) so as to generate output sample information. Theaddresses within the reference picture memory (457) from where themotion compensation prediction unit (453) fetches prediction samples canbe controlled by motion vectors, available to the motion compensationprediction unit (453) in the form of symbols (421) that can have, forexample X, Y, and reference picture components. Motion compensation alsocan include interpolation of sample values as fetched from the referencepicture memory (457) when sub-sample exact motion vectors are in use,motion vector prediction mechanisms, and so forth.

The output samples of the aggregator (455) can be subject to variousloop filtering techniques in the loop filter unit (456). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video sequence (alsoreferred to as coded video bitstream) and made available to the loopfilter unit (456) as symbols (421) from the parser (420), but can alsobe responsive to meta-information obtained during the decoding ofprevious (in decoding order) parts of the coded picture or coded videosequence, as well as responsive to previously reconstructed andloop-filtered sample values.

The output of the loop filter unit (456) can be a sample stream that canbe output to the render device (412) as well as stored in the referencepicture memory (457) for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. For example, once a codedpicture corresponding to a current picture is fully reconstructed andthe coded picture has been identified as a reference picture (by, forexample, the parser (420)), the current picture buffer (458) can becomea part of the reference picture memory (457), and a fresh currentpicture buffer can be reallocated before commencing the reconstructionof the following coded picture.

The video decoder (410) may perform decoding operations according to apredetermined video compression technology in a standard, such as ITU-TRec. H.265. The coded video sequence may conform to a syntax specifiedby the video compression technology or standard being used, in the sensethat the coded video sequence adheres to both the syntax of the videocompression technology or standard and the profiles as documented in thevideo compression technology or standard. Specifically, a profile canselect certain tools as the only tools available for use under thatprofile from all the tools available in the video compression technologyor standard. Also necessary for compliance can be that the complexity ofthe coded video sequence is within bounds as defined by the level of thevideo compression technology or standard. In some cases, levels restrictthe maximum picture size, maximum frame rate, maximum reconstructionsample rate (measured in, for example megasamples per second), maximumreference picture size, and so on. Limits set by levels can, in somecases, be further restricted through Hypothetical Reference Decoder(HRD) specifications and metadata for HRD buffer management signaled inthe coded video sequence.

In an embodiment, the receiver (431) may receive additional (redundant)data with the encoded video. The additional data may be included as partof the coded video sequence(s). The additional data may be used by thevideo decoder (410) to properly decode the data and/or to moreaccurately reconstruct the original video data. Additional data can bein the form of, for example, temporal, spatial, or signal noise ratio(SNR) enhancement layers, redundant slices, redundant pictures, forwarderror correction codes, and so on.

FIG. 5 shows a block diagram of a video encoder (503) according to anembodiment of the present disclosure. The video encoder (503) isincluded in an electronic device (520). The electronic device (520)includes a transmitter (540)(e.g., transmitting circuitry). The videoencoder (503) can be used in the place of the video encoder (303) in theFIG. 3 example.

The video encoder (503) may receive video samples from a video source(501) (that is not part of the electronic device (520) in the FIG. 5example) that may capture video image(s) to be coded by the videoencoder (503). In another example, the video source (501) is a part ofthe electronic device (520).

The video source (501) may provide the source video sequence to be codedby the video encoder (503) in the form of a digital video sample streamthat can be of any suitable bit depth (for example: 8 bit, 10 bit, 12bit, . . . ), any colorspace (for example, BT.601 Y CrCB, RGB, . . . ),and any suitable sampling structure (for example Y CrCb 4:2:0, Y CrCb4:4:4). In a media serving system, the video source (501) may be astorage device storing previously prepared video. In a videoconferencingsystem, the video source (501) may be a camera that captures local imageinformation as a video sequence. Video data may be provided as aplurality of individual pictures that impart motion when viewed insequence. The pictures themselves may be organized as a spatial array ofpixels, wherein each pixel can comprise one or more samples depending onthe sampling structure, color space, etc. in use. A person skilled inthe art can readily understand the relationship between pixels andsamples. The description below focuses on samples.

According to an embodiment, the video encoder (503) may code andcompress the pictures of the source video sequence into a coded videosequence (543) in real time or under any other time constraints asrequired by the application. Enforcing appropriate coding speed is onefunction of a controller (550). In some embodiments, the controller(550) controls other functional units as described below and isfunctionally coupled to the other functional units. The coupling is notdepicted for clarity. Parameters set by the controller (550) can includerate control related parameters (picture skip, quantizer, lambda valueof rate-distortion optimization techniques, . . . ), picture size, groupof pictures (GOP) layout, maximum motion vector search range, and soforth. The controller (550) can be configured to have other suitablefunctions that pertain to the video encoder (503) optimized for acertain system design.

In some embodiments, the video encoder (503) is configured to operate ina coding loop. As an oversimplified description, in an example, thecoding loop can include a source coder (530) (e.g., responsible forcreating symbols, such as a symbol stream, based on an input picture tobe coded, and a reference picture(s)), and a (local) decoder (533)embedded in the video encoder (503). The decoder (533) reconstructs thesymbols to create the sample data in a similar manner as a (remote)decoder also would create (as any compression between symbols and codedvideo bitstream is lossless in the video compression technologiesconsidered in the disclosed subject matter). The reconstructed samplestream (sample data) is input to the reference picture memory (534). Asthe decoding of a symbol stream leads to bit-exact results independentof decoder location (local or remote), the content in the referencepicture memory (534) is also bit exact between the local encoder andremote encoder. In other words, the prediction part of an encoder “sees”as reference picture samples exactly the same sample values as a decoderwould “see” when using prediction during decoding. This fundamentalprinciple of reference picture synchronicity (and resulting drift, ifsynchronicity cannot be maintained, for example because of channelerrors) is used in some related arts as well.

The operation of the “local” decoder (533) can be the same as of a“remote” decoder, such as the video decoder (410), which has alreadybeen described in detail above in conjunction with FIG. 4. Brieflyreferring also to FIG. 4, however, as symbols are available andencoding/decoding of symbols to a coded video sequence by an entropycoder (545) and the parser (420) can be lossless, the entropy decodingparts of the video decoder (410), including the buffer memory (415), andparser (420) may not be fully implemented in the local decoder (533).

An observation that can be made at this point is that any decodertechnology except the parsing/entropy decoding that is present in adecoder also necessarily needs to be present, in substantially identicalfunctional form, in a corresponding encoder. For this reason, thedisclosed subject matter focuses on decoder operation. The descriptionof encoder technologies can be abbreviated as they are the inverse ofthe comprehensively described decoder technologies. Only in certainareas a more detail description is required and provided below.

During operation, in some examples, the source coder (530) may performmotion compensated predictive coding, which codes an input picturepredictively with reference to one or more previously-coded picture fromthe video sequence that were designated as “reference pictures”. In thismanner, the coding engine (532) codes differences between pixel blocksof an input picture and pixel blocks of reference picture(s) that may beselected as prediction reference(s) to the input picture.

The local video decoder (533) may decode coded video data of picturesthat may be designated as reference pictures, based on symbols createdby the source coder (530). Operations of the coding engine (532) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 5), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (533) replicates decodingprocesses that may be performed by the video decoder on referencepictures and may cause reconstructed reference pictures to be stored inthe reference picture cache (534). In this manner, the video encoder(503) may store copies of reconstructed reference pictures locally thathave common content as the reconstructed reference pictures that will beobtained by a far-end video decoder (absent transmission errors).

The predictor (535) may perform prediction searches for the codingengine (532). That is, for a new picture to be coded, the predictor(535) may search the reference picture memory (534) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture motion vectors, block shapes, and so on, that may serve as anappropriate prediction reference for the new pictures. The predictor(535) may operate on a sample block-by-pixel block basis to findappropriate prediction references. In some cases, as determined bysearch results obtained by the predictor (535), an input picture mayhave prediction references drawn from multiple reference pictures storedin the reference picture memory (534).

The controller (550) may manage coding operations of the source coder(530), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (545). The entropy coder (545)translates the symbols as generated by the various functional units intoa coded video sequence, by lossless compressing the symbols according totechnologies such as Huffman coding, variable length coding, arithmeticcoding, and so forth.

The transmitter (540) may buffer the coded video sequence(s) as createdby the entropy coder (545) to prepare for transmission via acommunication channel (560), which may be a hardware/software link to astorage device which would store the encoded video data. The transmitter(540) may merge coded video data from the video coder (503) with otherdata to be transmitted, for example, coded audio data and/or ancillarydata streams (sources not shown).

The controller (550) may manage operation of the video encoder (503).During coding, the controller (550) may assign to each coded picture acertain coded picture type, which may affect the coding techniques thatmay be applied to the respective picture. For example, pictures oftenmay be assigned as one of the following picture types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other picture in the sequence as a source ofprediction. Some video codecs allow for different types of intrapictures, including, for example Independent Decoder Refresh (“IDR”)Pictures. A person skilled in the art is aware of those variants of Ipictures and their respective applications and features.

A predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A bi-directionally predictive picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of 1 pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded predictively, viaspatial prediction or via temporal prediction with reference to onepreviously coded reference picture. Blocks of B pictures may be codedpredictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video encoder (503) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video encoder (503) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

In an embodiment, the transmitter (540) may transmit additional datawith the encoded video. The source coder (530) may include such data aspart of the coded video sequence. Additional data may comprisetemporal/spatial/SNR enhancement layers, other forms of redundant datasuch as redundant pictures and slices, SEI messages, VUI parameter setfragments, and so on.

A video may be captured as a plurality of source pictures (videopictures) in a temporal sequence. Intra-picture prediction (oftenabbreviated to intra prediction) makes use of spatial correlation in agiven picture, and inter-picture prediction makes uses of the (temporalor other) correlation between the pictures. In an example, a specificpicture under encoding/decoding, which is referred to as a currentpicture, is partitioned into blocks. When a block in the current pictureis similar to a reference block in a previously coded and still bufferedreference picture in the video, the block in the current picture can becoded by a vector that is referred to as a motion vector. The motionvector points to the reference block in the reference picture, and canhave a third dimension identifying the reference picture, in casemultiple reference pictures are in use.

In some embodiments, a bi-prediction technique can be used in theinter-picture prediction. According to the bi-prediction technique, tworeference pictures, such as a first reference picture and a secondreference picture that are both prior in decoding order to the currentpicture in the video (but may be in the past and future, respectively,in display order) are used. A block in the current picture can be codedby a first motion vector that points to a first reference block in thefirst reference picture, and a second motion vector that points to asecond reference block in the second reference picture. The block can bepredicted by a combination of the first reference block and the secondreference block.

Further, a merge mode technique can be used in the inter-pictureprediction to improve coding efficiency.

According to some embodiments of the disclosure, predictions, such asinter-picture predictions and intra-picture predictions are performed inthe unit of blocks. For example, according to the HEVC standard, apicture in a sequence of video pictures is partitioned into coding treeunits (CTU) for compression, the CTUs in a picture have the same size,such as 64×64 pixels, 32×32 pixels, or 16×16 pixels. In general, a CTUincludes three coding tree blocks (CTBs), which are one luma CTB and twochroma CTBs. Each CTU can be recursively quadtree split into one ormultiple coding units (CUs). For example, a CTU of 64×64 pixels can besplit into one CU of 64×64 pixels, or 4 CUs of 32×32 pixels, or 16 CUsof 16×16 pixels. In an example, each CU is analyzed to determine aprediction type for the CU, such as an inter prediction type or an intraprediction type. The CU is split into one or more prediction units (PUs)depending on the temporal and/or spatial predictability. Generally, eachPU includes a luma prediction block (PB), and two chroma PBs. In anembodiment, a prediction operation in coding (encoding/decoding) isperformed in the unit of a prediction block. Using a luma predictionblock as an example of a prediction block, the prediction block includesa matrix of values (e.g., luma values) for pixels, such as 8×8 pixels,16×16 pixels, 8×16 pixels, 16×8 pixels, and the like.

FIG. 6 shows a diagram of a video encoder (603) according to anotherembodiment of the disclosure. The video encoder (603) is configured toreceive a processing block (e.g., a prediction block) of sample valueswithin a current video picture in a sequence of video pictures, andencode the processing block into a coded picture that is part of a codedvideo sequence. In an example, the video encoder (603) is used in theplace of the video encoder (303) in the FIG. 3 example.

In an HEVC example, the video encoder (603) receives a matrix of samplevalues for a processing block, such as a prediction block of 8×8samples, and the like. The video encoder (603) determines whether theprocessing block is best coded using intra mode, inter mode, orbi-prediction mode using, for example, rate-distortion optimization.When the processing block is to be coded in intra mode, the videoencoder (603) may use an intra prediction technique to encode theprocessing block into the coded picture; and when the processing blockis to be coded in inter mode or bi-prediction mode, the video encoder(603) may use an inter prediction or bi-prediction technique,respectively, to encode the processing block into the coded picture. Incertain video coding technologies, merge mode can be an inter pictureprediction submode where the motion vector is derived from one or moremotion vector predictors without the benefit of a coded motion vectorcomponent outside the predictors. In certain other video codingtechnologies, a motion vector component applicable to the subject blockmay be present. In an example, the video encoder (603) includes othercomponents, such as a mode decision module (not shown) to determine themode of the processing blocks.

In the FIG. 6 example, the video encoder (603) includes the interencoder (630), an intra encoder (622), a residue calculator (623), aswitch (626), a residue encoder (624), a general controller (621), andan entropy encoder (625) coupled together as shown in FIG. 6.

The inter encoder (630) is configured to receive the samples of thecurrent block (e.g., a processing block), compare the block to one ormore reference blocks in reference pictures (e.g., blocks in previouspictures and later pictures), generate inter prediction information(e.g., description of redundant information according to inter encodingtechnique, motion vectors, merge mode information), and calculate interprediction results (e.g., predicted block) based on the inter predictioninformation using any suitable technique. In some examples, thereference pictures are decoded reference pictures that are decoded basedon the encoded video information.

The intra encoder (622) is configured to receive the samples of thecurrent block (e.g., a processing block), in some cases compare theblock to blocks already coded in the same picture, generate quantizedcoefficients after transform, and in some cases also intra predictioninformation (e.g., an intra prediction direction information accordingto one or more intra encoding techniques). In an example, the intraencoder (622) also calculates intra prediction results (e.g., predictedblock) based on the intra prediction information and reference blocks inthe same picture.

The general controller (621) is configured to determine general controldata and control other components of the video encoder (603) based onthe general control data. In an example, the general controller (621)determines the mode of the block, and provides a control signal to theswitch (626) based on the mode. For example, when the mode is the intramode, the general controller (621) controls the switch (626) to selectthe intra mode result for use by the residue calculator (623), andcontrols the entropy encoder (625) to select the intra predictioninformation and include the intra prediction information in thebitstream; and when the mode is the inter mode, the general controller(621) controls the switch (626) to select the inter prediction resultfor use by the residue calculator (623), and controls the entropyencoder (625) to select the inter prediction information and include theinter prediction information in the bitstream.

The residue calculator (623) is configured to calculate a difference(residue data) between the received block and prediction resultsselected from the intra encoder (622) or the inter encoder (630). Theresidue encoder (624) is configured to operate based on the residue datato encode the residue data to generate the transform coefficients. In anexample, the residue encoder (624) is configured to convert the residuedata from a spatial domain to a frequency domain, and generate thetransform coefficients. The transform coefficients are then subject toquantization processing to obtain quantized transform coefficients. Invarious embodiments, the video encoder (603) also includes a residuedecoder (628). The residue decoder (628) is configured to performinverse-transform, and generate the decoded residue data. The decodedresidue data can be suitably used by the intra encoder (622) and theinter encoder (630). For example, the inter encoder (630) can generatedecoded blocks based on the decoded residue data and inter predictioninformation, and the intra encoder (622) can generate decoded blocksbased on the decoded residue data and the intra prediction information.The decoded blocks are suitably processed to generate decoded picturesand the decoded pictures can be buffered in a memory circuit (not shown)and used as reference pictures in some examples.

The entropy encoder (625) is configured to format the bitstream toinclude the encoded block. The entropy encoder (625) is configured toinclude various information according to a suitable standard, such asthe HEVC standard. In an example, the entropy encoder (625) isconfigured to include the general control data, the selected predictioninformation (e.g., intra prediction information or inter predictioninformation), the residue information, and other suitable information inthe bitstream. Note that, according to the disclosed subject matter,when coding a block in the merge submode of either inter mode orbi-prediction mode, there is no residue information.

FIG. 7 shows a diagram of a video decoder (710) according to anotherembodiment of the disclosure. The video decoder (710) is configured toreceive coded pictures that are part of a coded video sequence, anddecode the coded pictures to generate reconstructed pictures. In anexample, the video decoder (710) is used in the place of the videodecoder (310) in the FIG. 3 example.

In the FIG. 7 example, the video decoder (710) includes an entropydecoder (771), an inter decoder (780), a residue decoder (773), areconstruction module (774), and an intra decoder (772) coupled togetheras shown in FIG. 7.

The entropy decoder (771) can be configured to reconstruct, from thecoded picture, certain symbols that represent the syntax elements ofwhich the coded picture is made up. Such symbols can include, forexample, the mode in which a block is coded (such as, for example, intramode, inter mode, bi-predicted mode, the latter two in merge submode oranother submode), prediction information (such as, for example, intraprediction information or inter prediction information) that canidentify certain sample or metadata that is used for prediction by theintra decoder (772) or the inter decoder (780), respectively, residualinformation in the form of, for example, quantized transformcoefficients, and the like. In an example, when the prediction mode isinter or bi-predicted mode, the inter prediction information is providedto the inter decoder (780); and when the prediction type is the intraprediction type, the intra prediction information is provided to theintra decoder (772). The residual information can be subject to inversequantization and is provided to the residue decoder (773).

The inter decoder (780) is configured to receive the inter predictioninformation, and generate inter prediction results based on the interprediction information.

The intra decoder (772) is configured to receive the intra predictioninformation, and generate prediction results based on the intraprediction information.

The residue decoder (773) is configured to perform inverse quantizationto extract de-quantized transform coefficients, and process thede-quantized transform coefficients to convert the residual from thefrequency domain to the spatial domain. The residue decoder (773) mayalso require certain control information (to include the QuantizerParameter (QP)), and that information may be provided by the entropydecoder (771) (data path not depicted as this may be low volume controlinformation only).

The reconstruction module (774) is configured to combine, in the spatialdomain, the residual as output by the residue decoder (773) and theprediction results (as output by the inter or intra prediction modulesas the case may be) to form a reconstructed block, that may be part ofthe reconstructed picture, which in turn may be part of thereconstructed video. It is noted that other suitable operations, such asa deblocking operation and the like, can be performed to improve thevisual quality.

It is noted that the video encoders (303), (503), and (603), and thevideo decoders (310), (410), and (710) can be implemented using anysuitable technique. In an embodiment, the video encoders (303), (503),and (603), and the video decoders (310), (410), and (710) can beimplemented using one or more integrated circuits. In anotherembodiment, the video encoders (303), (503), and (503), and the videodecoders (310), (410), and (710) can be implemented using one or moreprocessors that execute software instructions.

II. Inter Picture Prediction Modes

In various embodiments, a picture can be partitioned into blocks, forexample, using a tree structure based partition scheme. The resultingblocks can then be processed with different processing modes, such as anintra prediction mode, an inter prediction mode (e.g., merge mode, skipmode, advanced motion vector prediction (AVMP) mode), and the like. Anintra coded block can be a block that is coded with an intra predictionmode. In contrast, an inter coded block can be a bock that is processedwith an inter prediction mode.

1. Regular Merge Mode

When a currently processed block, referred to as a current block, isprocessed with a merge mode, a neighboring block can be selected from aspatial or temporal neighborhood of the current block. The current blockcan be merged with the selected neighboring block by sharing a same setof motion data (or referred to as motion information) from the selectedneighboring block. This merge mode operation can be performed over agroup of neighboring blocks, such that a region of neighboring blockscan be merged together and share a same set of motion data. Duringtransmission from an encoder to a decoder, an index indicating themotion data of the selected neighboring block can be transmitted for thecurrent block, instead of transmission of the whole set of motion data.In this way, an amount of data (bits) that are used for transmission ofmotion information can be reduced, and coding efficiency can beimproved.

In the above example, the neighboring block, which provides the motiondata, can be selected from a set of candidate positions. The candidatepositions can be predefined with respect to the current block. Forexample, the candidate positions can include spatial candidate positionsand temporal candidate positions. Each spatial candidate position isassociated with a spatial neighboring block neighboring the currentblock. Each temporal candidate position is associated with a temporalneighboring block located in another coded picture (e.g., a previouslycoded picture). Neighboring blocks overlapping the candidate positions(referred to as candidate blocks) are a subset of all the spatial ortemporal neighboring blocks of the current block. In this way, thecandidate blocks can be evaluated for selection of a to-be-merged blockinstead of the whole set of neighboring blocks.

FIG. 8 shows an example of candidate positions. From those candidatepositions, a set of merge candidates can be selected to construct amerge candidate list. As shown, a current block (810) is to be processedwith merge mode. A set of candidate positions {A1, B1, B0, A0, B2, C0,C1} are defined for the merge mode processing. Specifically, candidatepositions {A1, B1, B0, A0, B2} are spatial candidate positions thatrepresent positions of candidate blocks that are in the same picture asthe current block (810). In contrast, candidate positions {C0, C1} aretemporal candidate positions that represent positions of candidateblocks that are in another coded picture and neighbor or overlap aco-located block of the current block (810). As shown, the candidateposition C1 can be located near (e.g., adjacent to) a center of thecurrent block (810).

A candidate position can be represented by a block of samples or asample in different examples. In FIG. 8, each candidate position isrepresented by a block of samples, for example, having a size of 4×4samples. A size of such a block of samples corresponding to a candidateposition can be equal to or smaller than a minimum allowable size of PBs(e.g., 4×4 samples) defined for a tree-based partitioning scheme usedfor generating the current block (810). Under such a configuration, ablock corresponding to a candidate position can always be covered withina single neighboring PB. In an alternative example, a sample position(e.g., a bottom-right sample within the block A1, or a top-right samplewithin the block A0) may be used to represent a candidate position. Sucha sample is referred to as a representative sample, while such aposition is referred to as a representative position.

In one example, based on the candidate positions {A1, B1, B0, A0, B2,C0, C1} defined in FIG. 8, a merge mode process can be performed toselect merge candidates from the candidate positions {A1, B1, B0, A0,B2, C0, C1} to construct a candidate list. The candidate list can have apredefined maximum number of merge candidates, represented as Cm. Eachmerge candidate in the candidate list can include a set of motion datathat can be used for motion-compensated prediction.

The merge candidates can be listed in the candidate list according to acertain order. For example, depending on how the merge candidate isderived, different merge candidates may have different probabilities ofbeing selected. The merge candidates having higher probabilities ofbeing selected are positioned in front of the merge candidates havinglower probabilities of being selected. Based on such an order, eachmerge candidate is associated with an index (referred to as a mergeindex). In one embodiment, a merge candidate having a higher probabilityof being selected will have a smaller index value such that fewer bitsare needed for coding the respective index.

In one example, the motion data of a merge candidate can includehorizontal and vertical motion vector displacement values of one or twomotion vectors, one or two reference picture indices associated with theone or two motion vectors, and optionally an identification of whichreference picture list is associated with an reference picture index.

In an example, according to a predefined order, a first number of mergecandidates, Ca, is derived from the spatial candidate positionsaccording to the order {A1, B1, B0, A0, B2}, and a second number ofmerge candidates, Cb=Cm−Ca, is derived from the temporal candidatepositions according to the order {C0, C1}. The numerals A1, B1, B0, A0,B2, C0, C1 for representing candidate positions can also be used torefer to merge candidates. For example, a merge candidate obtained fromcandidate position A1 is referred to as the merge candidate A1.

In some scenarios, a merge candidate at a candidate position may beunavailable. For example, a candidate block at a candidate position canbe intra-predicted, outside of a slice or tile including the currentblock (810), or not in a same coding tree block (CTB) row as the currentblock (810). In some scenarios, a merge candidate at a candidateposition may be redundant. For example, one neighboring block of thecurrent block (810) can overlap two candidate positions. The redundantmerge candidate can be removed from the candidate list (e.g., byperforming a pruning process). When a total number of available mergecandidates (with redundant candidates being removed) in the candidatelist is smaller than the maximum number of merge candidates Cm,additional merge candidates can be generated (e.g., according to apreconfigured rule) to fill the candidate list such that the candidatelist can be maintained to have a fixed length. For example, additionalmerge candidates can include combined bi-predictive candidates and zeromotion vector candidates.

After the candidate list is constructed, at an encoder, an evaluationprocess can be performed to select a merge candidate from the candidatelist. For example, rate-distortion (RD) performance corresponding toeach merge candidate can be calculated, and the one with the best RDperformance can be selected. Accordingly, a merge index associated withthe selected merge candidate can be determined for the current block(810) and signaled to a decoder.

At a decoder, the merge index of the current block (810) can bereceived. A similar candidate list construction process, as describedabove, can be performed to generate a candidate list that is the same asthe candidate list generated at the encoder side. After the candidatelist is constructed, a merge candidate can be selected from thecandidate list based on the received merge index without performing anyfurther evaluations in some examples. Motion data of the selected mergecandidate can be used for a subsequent motion-compensated prediction ofthe current block (810).

A skip mode is also introduced in some examples. For example, in theskip mode, a current block can be predicted using a merge mode asdescribed above to determine a set of motion data, however, no residueis generated, and no transform coefficients are transmitted. A skip flagcan be associated with the current block. The skip flag and a mergeindex indicating the related motion information of the current block canbe signaled to a video decoder. For example, at the beginning of a CU inan inter-picture prediction slice, a skip flag can be signaled thatimplies the following: the CU only contains one PU (2N×2N); the mergemode is used to derive the motion data; and no residual data is presentin the bitstream. At the decoder side, based on the skip flag, aprediction block can be determined based on the merge index for decodinga respective current block without adding residue information. Thus,various methods for video coding with merge mode disclosed herein can beutilized in combination with a skip mode.

As an example, in an embodiment, when a merge flag or a skip flag issignaled as true in a bitstream, a merge index is then signaled toindicate which candidate in a merge candidate list will be used toprovide motion vectors for a current block. Up to four spatiallyneighboring motion vectors and up to one temporally neighboring motionvectors can be added to the merge candidate list. A syntaxMaxMergeCandsNum is defined as the size of the merge candidate list. Thesyntax MaxMergeVandsNum can be signaled in the bitstream.

2. Affine Merge Mode

FIG. 9 is a schematic illustration of spatial neighboring blocks and atemporal neighboring block of a current block (or referred to as acoding unit (CU)) (901) in accordance with an embodiment. As shown, thespatial neighboring blocks are denoted A0, A1, A2, B0, B1, B2, and B3(902, 903, 907, 904, 905, 906, and 908, respectively), and the temporalneighboring block are denoted C0 (912). In some examples, the spatialneighboring blocks A0, A1, A2, B0, B1, B2, and B3 and the current block(901) belong to a same picture. In some examples, the temporalneighboring block C0 belongs to a reference picture and corresponds to aposition outside the current block (901) and adjacent to a lower-rightcorner of the current block (901).

In some examples, a motion vector of the current block (901) and/orsub-blocks of the current block can be derived using an affine model(e.g., a 6-parameter affine model or a 4-parameter affine model). Insome examples, an affine model has 6 parameters (e.g., a 6-parameteraffine model) to describe the motion vector of a block. In an example,the 6 parameters of an affine coded block can be represented by threemotion vectors (also referred to as three control point motionvectors(CPMVs)) at three different locations of the block (e.g., controlpoints CP0, CP1, and CP2 at upper-left, upper-right, and lower-leftcorners in FIG. 9). In another example, a simplified affine model usesfour parameters to describe the motion information of an affine codedblock, which can be represented by two motion vectors (also referred toas two CPMVs) at two different locations of the block (e.g., controlpoints CP0 and CP1 at upper-left and upper-right corners in FIG. 9).

A list of motion information candidates (also referred to as an affinemerge candidate list) can be constructed using an affine merge modebased on motion information of one or more of the spatial neighboringblocks and/or temporal neighboring blocks. In some examples, the affinemerge mode can be applied when the current block (901) has a width andheight that are equal to or greater than 8 samples. According to theaffine merge mode, the CPMVs of the current block (901) can bedetermined based on the motion information candidates on the list. Insome examples, the list of motion information candidates can include upto five CPMV candidates, and an index can be signaled to indicate whichCPMV candidate is to be used for the current block.

In some embodiments, the affine merge candidate list can have threetypes of CPVM candidates, including inherited affine candidates,constructed affine candidates, and a zero MV. An inherited affinecandidate can be derived by extrapolation from the CPMVs of theneighboring blocks. A constructed affine candidate can be derived usingthe translational MVs of the neighboring blocks.

In an example, there can be at most two inherited affine candidates,which are derived from corresponding affine motion models of theneighboring blocks, including one block from left neighboring blocks (A0and A1) and one from upper neighboring blocks (B0, B1, and B2). For thecandidate from the left, neighboring blocks A0 and A1 can besequentially checked, and a first available inherited affine candidatefrom neighboring blocks A0 and A1 is used as the inherited affinecandidate from the left. For the candidate from the top, neighboringblocks B0, B1, and B2 can be sequentially checked, and a first availableinherited affine candidate from neighboring blocks B0, B1, and B2 isused as the inherited affine candidate from the top. In some examples,no pruning check is performed between the two inherited affinecandidates.

When a neighboring affine block is identified, a corresponding inheritedaffine candidate to be added to the affine merge list of the currentblock (901) can be derived from the control point motion vectors of theneighboring affine block. In the FIG. 9 example, if the neighboringblock A1 is coded in affine mode, the motion vectors of the upper-leftcorner (control point CP0 _(A1)), the upper-right corner (control pointCP1 _(A1)), and the lower-left corner (control point CP2 _(A1)) of blockA1 can be obtained. When block A1 is coded using a 4-parameter affinemodel, the two CPMVs as an inherited affine candidate of the currentblock (901) can be calculated according to the motion vectors of controlpoint CP0 _(A1) and control point CP1 _(A1). When block A1 is codedusing a 6-parameter affine model, the three CPMVs as an inherited affinecandidate of the current block (901) can be calculated according to themotion vectors of control point CP0 _(A1), control point CP1 _(A1), andcontrol point CP2 _(A1).

Moreover, a constructed affine candidate can be derived by combining theneighboring translational motion information of each control point. Themotion information for the control points CP0, CP1, and CP2 is derivedfrom the specified spatial neighboring blocks A0, A1, A2, B0, B1, B2,and B3.

For example, CPMV_(k) (k=1, 2, 3, 4) represents the motion vector of thek-th control point, where CPMV₁ corresponds to control point CP0, CPMV₂corresponds to control point CP1, CPMV₃ corresponds to control pointCP2, and CPMV₄ corresponds to a temporal control point based on temporalneighboring block C0. For CPMV₁, neighboring blocks B2, B3, and A2 canbe sequentially checked, and a first available motion vector fromneighboring blocks B2, B3, and A2 is used as CPMV₁. For CPMV₂,neighboring blocks B1 and B0 can be sequentially checked, and a firstavailable motion vector from neighboring blocks B1 and B0 is used asCPMV₂. For CPMV₃, neighboring blocks A1 and A0 can be sequentiallychecked, and a first available motion vector from neighboring blocks A1and A0 is used as CPMV₃. Moreover, the motion vector of temporalneighboring block C0 can be used as CPMV₄, if available.

After CPMV₁, CPMV₂, CPMV₃, and CPMV₄, of four control points CP0, CP1,CP2 and the temporal control point are obtained, an affine mergecandidate list can be constructed to include affine merge candidatesthat are constructed in an order of: {CPMV₁, CPMV₂, CPMV₃}, {CPMV₁,CPMV₂, CPMV₄}, {CPMV₁, CPMV₃, CPMV₄}, {CPMV₂, CPMV₃, CPMV₄}, {CPMV₁,CPMV₂}, and {CPMV₁, CPMV₃}. Any combination of three CPMVs can form a6-parameter affine merge candidate, and any combination of two CPMVs canform a 4-parameter affine merge candidate. In some examples, in order toavoid a motion scaling process, if the reference indices of a group ofcontrol points are different, the corresponding combination of CPMVs canbe discarded.

3. Subblock-Based Temporal Motion Vector Prediction (SbTMVP) Mode

FIG. 10A is a schematic illustration of spatial neighboring blocks thatcan be used to determine predicting motion information for a currentblock (1011) using a sub-block based temporal MV prediction (SbTMVP)method based on motion information of the spatial neighboring blocks inaccordance with one embodiment. FIG. 10A shows a current block (1011)and its spatial neighboring blocks denoted A0, A1, B0, and B1 (1012,1013, 1014, and 1015, respectively). In some examples, spatialneighboring blocks A0, A1, B0, and B1 and the current block (1011)belong to a same picture.

FIG. 10B is a schematic illustration of determining motion informationfor sub-blocks of the current block (1011) using the SbTMVP method basedon a selected spatial neighboring block, such as block A1 in thisnon-limiting example, in accordance with an embodiment. In this example,the current block (1011) is in a current picture (1010), and a referenceblock (1061) is in a reference picture (1060) and can be identifiedbased on a motion shift (or displacement) between the current block(1011) and the reference block (1061) indicated by a motion vector(1022).

In some embodiments, similar to a temporal motion vector prediction(TMVP) in HEVC, a SbTMVP uses the motion information in variousreference sub-blocks in a reference picture for a current block in acurrent picture. In some embodiments, the same reference picture used byTMVP can be used for SbTVMP. In some embodiments, TMVP predicts motioninformation at a CU level but SbTMVP predicts motion at a sub-CU level.In some embodiments, TMVP uses the temporal motion vectors fromcollocated block in the reference picture, which has a correspondingposition adjacent to a lower-right corner or a center of a currentblock, and SbTMVP uses the temporal motion vectors from a referenceblock, which can be identified by performing a motion shift based on amotion vector from one of the spatial neighboring blocks of the currentblock.

For example, as shown in FIG. 10A, neighboring blocks A1, B1, B0, and A0can be sequentially checked in a SbTVMP process. As soon as a firstspatial neighboring block that has a motion vector that uses thereference picture (1060) as its reference picture is identified, such asblock A1 having the motion vector (1022) that points to a referenceblock AR1 in the reference picture (1060) for example, this motionvector (1022) can be used for performing the motion shift. If no suchmotion vector is available from the spatial neighboring blocks A1, B1,B0, and A0, the motion shift is set to (0, 0).

After determining the motion shift, the reference block (1061) can beidentified based on a position of the current block (1011) and thedetermined motion shift. In FIG. 10B, the reference block (1061) can befurther divided into 16 sub-blocks with reference motion information MRathrough MRp. In some examples, the reference motion information for eachsub-block in the reference block (1061) can be determined based on asmallest motion grid that covers a center sample of such sub-block. Themotion information can include motion vectors and correspondingreference indices. The current block (1011) can be further divided into16 sub-blocks, and the motion information MVa through MVp for thesub-blocks in the current block (1011) can be derived from the referencemotion information MRa through MRp in a manner similar to the TMVPprocess, with temporal scaling in some examples.

The sub-block size used in the SbTMVP process can be fixed (or otherwisepredetermined) or signaled. In some examples, the sub-block size used inthe SbTMVP process can be 8×8 samples. In some examples, the SbTMVPprocess is only applicable to a block with a width and height equal toor greater than the fixed or signaled size, for example 8 pixels.

In an example, a combined sub-block based merge list which contains aSbTVMP candidate and affine merge candidates is used for the signalingof a sub-block based merge mode. The SbTVMP mode can be enabled ordisabled by a sequence parameter set (SPS) flag. In some examples, ifthe SbTMVP mode is enabled, the SbTMVP candidate is added as the firstentry of the list of sub-block based merge candidates, and followed bythe affine merge candidates. In some embodiments, the maximum allowedsize of the sub-block based merge list is set to five. However, othersizes may be utilized in other embodiments.

In some embodiments, the encoding logic of the additional SbTMVP mergecandidate is the same as for the other merge candidates. That is, foreach block in a P or B slice, an additional rate-distortion check can beperformed to determine whether to use the SbTMVP candidate.

4. History-Based Motion Vector Prediction (HMVP) Mode

FIG. 11A is a flow chart outlining a process (1100) of constructing andupdating a list of motion information candidates using a history basedMV prediction (HMVP) method in accordance with one embodiment.

In some embodiments, a list of motion information candidates using theHMVP method Error! Reference source not found. can be constructed andupdated during an encoding or decoding process. The list can be referredto as a history list. The history list can be stored in forms of an HMVPtable or an HMVP buffer. The history list can be emptied when a newslice begins. In some embodiments, whenever there is an inter-codednon-affine block that is just encoded or decoded, the associated motioninformation can be added to a last entry of the history list as a newHMVP candidate. Therefore, before processing (encoding or decoding) acurrent block, the history list with HMVP candidates can be loaded(S1112). The current block can be encoded or decoded using the HMVPcandidates in the history list (S1114). Afterwards, the history list canbe updated using the motion information for encoding or decoding thecurrent block (S1116).

FIG. 11B is a schematic illustration of updating the list of motioninformation candidates using the history based MV prediction method inaccordance with one embodiment. FIG. 11B shows a history list having asize of L, where each candidate in the list can be identified with anindex ranging from 0 to L−1. L is an integer equal to or greater than 0.Before encoding or decoding a current block, the history list (1120)includes L candidates HMVP₀, HMVP₁, HMVP₂, . . . HMVP_(m), . . . ,HMVP_(L-2), and HMVP_(L-1), where m is an integer ranging from 0 to L.After encoding or decoding a current block, a new entry HMVP_(C) is tobe added to the history list.

In an example, the size of the history list can be set to 6, whichindicates up to 6 HMVP candidates can be added to the history list. Wheninserting a new motion candidate (e.g., HMVP_(C)) to the history list, aconstrained first-in-first-out (FIFO) rule can be utilized, wherein aredundancy check is first applied to find whether there is a redundantHMVP in the history list. When no redundant HMVP is found, the firstHMVP candidate (HMVP₁ in FIG. 11B example, with index=0) is removed fromthe list, and all other HMVP candidates afterwards are moved forward,e.g., with indices reduced by 1. The new HMVP_(C) candidate can be addedto the last entry of the list (with index=L−1 in FIG. 11B for example),as shown in the resulting list (1130). On the other hand, if a redundantHMVP is found (such as HMVP₂ in FIG. 11B example), the redundant HMVP inthe history list is removed from the list, and all the HMVP candidatesafterwards are moved forward, e.g., with indices reduced by 1. The newHMVP_(C) candidate can be added to the last entry of the list (withindex=L−1 in FIG. 11B for example), as shown in the resulting list(1140).

In some examples, the HMVP candidates could be used in the mergecandidate list construction process. For example, the latest HMVPcandidates in the list can be checked in order and inserted into thecandidate list after a TMVP candidate. Pruning can be applied on theHMVP candidates against the spatial or temporal merge candidates, butnot the sub-block motion candidates (i.e., SbTMVP candidates) in someembodiments.

In some embodiments, to reduce the number of pruning operations, one ormore of the following rules can be followed:

-   -   (a) Number of HMPV candidates to be checked denoted by M is set        as follows:        -   M=(N<=4)?L:(8−N),    -   wherein N indicates a number of available non-sub block merge        candidates, and L indicates number of available HMVP candidates        in the history list.    -   (b) In addition, once the total number of available merge        candidates becomes only one less than a signaled maximum number        of merge candidates, the merge candidate list construction        process from HMVP list can be terminated.    -   (c) Moreover, the number of pairs for combined bi-predictive        merge candidate derivation can be reduced from 12 to 6.

In some embodiments, HMVP candidates can be used in an AMVP candidatelist construction process. The motion vectors of the last K HMVPcandidates in the history list can be added to an AMVP candidate listafter a TMVP candidate. In some examples, only HMVP candidates with thesame reference picture as an AMVP target reference picture are to beadded to the AMVP candidate list. Pruning can be applied on the HMVPcandidates. In some examples, K is set to 4 while the AMVP list size iskept unchanged, e.g., equal to 2.

5. Pairwise Average Motion Vector Candidates

In some embodiments, pairwise average candidates can be generated byaveraging predefined pairs of candidates in a current merge candidatelist. For example, the predefined pairs are defined as {(0, 1), (0, 2),(1, 2), (0, 3), (1, 3), (2, 3)} in an embodiment, where the numbersdenote the merge indices to the merge candidate list. For example, theaveraged motion vectors are calculated separately for each referencepicture list. If both to-be-averaged motion vectors are available in onelist, these two motion vectors are averaged even when they point todifferent reference pictures. If only one motion vector is available,the available one can be used directly. If no motion vector isavailable, the respective pair is skipped in one example. The pairwiseaverage candidates replace the combined candidates in some embodimentsin constructing a merge candidate list.

6. Merge with Motion Vector Difference (MMVD) Mode

In some embodiments, a merge with motion vector difference (MMVD) modeis used for determining a motion vector predictor of a current block.The MMVD mode can be used when skip mode or merge mode is enabled. TheMMVD mode reuses merge candidates on a merge candidate list of the skipmode or merge mode. For example, a merge candidate selected from themerge candidate list can be used to provide a starting point at areference picture. A motion vector of the current block can be expressedwith the starting point and a motion offset including a motion magnitudeand a motion direction with respect to the starting point. At an encoderside, selection of the merge candidate and determination of the motionoffset can be based on a search process (an evaluation process). At adecoder side, the selected merge candidate and the motion offset can bedetermined based on signaling from the encoder side.

The MMVD mode can reuse a merge candidate list constructed in variousinter prediction modes described herein. In some examples, onlycandidates of a default merge type (e.g., MRG_TYPE_DEFAULT_N) on themerge candidate list are considered for MMVD mode. Examples of the mergecandidates of the default merge types can include (i) merge candidatesemployed in the merge mode, (ii) merge candidates from a history bufferin the HMVP mode, and (iii) pairwise average motion vector candidates asdescribed herein. Merge candidates in the affine mode or SbTMVP mode arenot used for expansion in MMVD mode in some examples.

A base candidate index (IDX) can be used to define the starting point.For example, a list of merge candidates (motion vector predicators(MVPs)) associated with indices from 0 to 3 is shown in Table 1. Themerge candidate having an index of the base candidate index can bedetermined from the list, and used to provide the starting point.

TABLE 1 Base candidate IDX Base candidate IDX 0 1 2 3 N^(th) MVP 1^(st)MVP 2^(nd) MVP 3^(rd) MVP 4^(th) MVP

A distance index can be used to provide motion magnitude information.For example, a plurality of predefined pixel distances are shown inTable 2 each associated with indices from 0 to 7. The pixel distancehaving an index of the distance index can be determined from theplurality of pixel distances, and used to provide the motion magnitude.

TABLE 2 Distance IDX Distance IDX 0 1 2 3 4 5 6 7 Pixel 1/4-pel 1/2-pel1-pel 2-pel 4-pel 8-pel 16-pel 32-pel distance

A direction index can be used to provide motion direction information.For example, four directions with indices from 00 to 11 (binary) areshown in Table 3. The direction with an index of the direction index canbe determined from the four directions, and used to provide a directionof the motion offset with respect to the starting point.

TABLE 3 Direction IDX Direction IDX 00 01 10 11 x-axis + − N/A N/Ay-axis N/A N/A + −

MMVD syntax elements can be transmitted in a bitstream to signal a setof MMVD indices including a base candidate index, a direction index, anda distance IDX in the MMVD mode.

In some embodiments, an MMVD enable flag is signaled after sending askip and merge flag for coding a current block. For example, when theskip and merge flag is true, the MMVD flag is parsed. When the MMVD flagis equal to 1, in an example, the MMVD syntax elements (the set of MMVDindices) are parsed. In one example, when the MMVD flag is not 1, a flagassociated with another mode, such as an AFFINE flag, is parsed. Whenthe AFFINE flag is equal to 1, the AFFINE mode is used for processingthe current block. When the AFFINE flag is not 1, in an example, askip/merge index is parsed for processing the current block withskip/merge mode.

FIGS. 12-13 show an example of a search process in MMVD mode accordingto an embodiment of the disclosure. By performing the search process, aset of MMVD indices including a base candidate index, a direction index,and a distance index can be determined for a current block (1201) in acurrent picture (or referred to as a current frame).

As shown in FIGS. 12-13, a first motion vector (1211) and a secondmotion vector (1221) belonging to a first merge candidate are shown. Thefirst merge candidate can be a merge candidate on a merge candidate listconstructed for the current block (1201). The first and second motionvectors (1211) and (1221) can be associated with two reference pictures(1202) and (1203) in reference picture lists L0 and L1, respectively.Accordingly, two starting points (1311) and (1321) in FIG. 13 can bedetermined at the reference pictures (1202) and (1203).

In an example, based on the starting points (1311) and (1321), multiplepredefined points extending from the starting points (1311) and (1321)in vertical directions (represented by +Y, or −Y) or horizontaldirections (represented by +X and −X) in the reference pictures (1202)and (1203) can be evaluated. In one example, a pair of points mirroringeach other with respect to the respective starting point (1311) or(1321), such as the pair of points (1314) and (1324), or the pair ofpoints (1315) and (1325), can be used to determine a pair of motionvectors which may form a motion vector predictor candidate for thecurrent block (1201). Those motion vector predictor candidatesdetermined based on the predefined points surrounding the startingpoints (1311) or (1321) can be evaluated.

In addition to the first merge candidate, other available or valid mergecandidates on the merge candidate list of the current block (1201) canalso be evaluated similarly. In one example, for a uni-predicted mergecandidate, only one prediction direction associated with one of the tworeference picture lists is evaluated.

Based on the evaluations, a best motion vector predictor candidate canbe determined. Accordingly, corresponding to the best motion vectorpredictor candidate, a best merge candidate can be selected from themerge list, and a motion direction and a motion distance can also bedetermined. For example, based on the selected merge candidate and theTable 1, a base candidate index can be determined. Based on the selectedmotion vector predictor, such as that corresponding to the predefinedpoint (1315) (or (1325)), a direction and a distance of the point (1315)with respect to the starting point (1311) can be determined. Accordingto Table 2 and Table 3, a direction index and a distance index canaccordingly be determined.

It is noted that the examples described above are merely forillustrative purpose. In alternative examples, based on the motionvector expression method provided in the MMVD mode, the motion distancesand motion directions may be defined differently. In addition, theevaluation process (search process) may be performed differently. Forexample, for a bi-prediction merge candidate, three types of predictiondirections (e.g., L0, L1, and L0 and L1) may be evaluated based on a setof predefined distances and directions to select a best motion vectorpredictor. For another example, a uni-predicted merge candidate may beconverted by mirroring or scaling to a bi-predicted merge candidate, andsubsequently evaluated. In the above examples, an additional syntaxindicating a prediction direction (e.g., L0, L1, or L0 and L1) resultingfrom the evaluation process may be signaled.

As described above, merge candidates on a merge candidate list areevaluated to determine a base candidate in the MMVD mode at an encoder.At a decoder, using a base candidate index as input, a motion vectorpredictor can be selected from a merge candidate list. Accordingly, noadditional line buffer is needed for the MMVD mode in addition to a linebuffer for storage of the merge candidates.

7. Affine Model Representation with Affine Parameter and Base MV

7.1 Affine Motion Derivation

With a 4-parameter affine model, a MV (mv^(h), mv^(v)) at a position (x,y) can be derived as

$\begin{matrix}\left\{ {\begin{matrix}{{{mv}^{h}\left( {x,y} \right)} = {{a\left( {x - x_{base}} \right)} - {b\left( {y - y_{base}} \right)} + {mv}_{base}^{h}}} \\{{{mv}^{v}\left( {x,y} \right)} = {{b\left( {x - x_{base}} \right)} + {a\left( {y - y_{base}} \right)} + {mv}_{base}^{v}}}\end{matrix}.} \right. & {{Equation}\mspace{14mu} 2.7{.1}}\end{matrix}$

With a 6-parameter affine model, a MV (mv^(h), mv^(v)) at a position (x,y) can be derived as

$\begin{matrix}\left\{ {\begin{matrix}{{{mv}^{h}\left( {x,y} \right)} = {{a\left( {x - x_{base}} \right)} + {c\left( {y - y_{base}} \right)} + {mv}_{base}^{h}}} \\{{{mv}^{v}\left( {x,y} \right)} = {{b\left( {x - x_{base}} \right)} + {d\left( {y - y_{base}} \right)} + {mv}_{base}^{v}}}\end{matrix}.} \right. & {{Equation}\mspace{14mu} 2.7{.2}}\end{matrix}$

In the above equations 2.7.1 and 2.7.2, MV_(base) (mv^(h) _(base),mv^(v) _(base)) is a base MV at a base position (x_(base), y_(base)),and (a, b), or (a, b, c, d) represent affine parameters for the4-parameter affine model and 6-parameter affine model, respectively. Theaffine parameters can be calculated as:

$\begin{matrix}{{a = \frac{\left( {{mv}_{1}^{h} - {mv}_{0}^{h}} \right)}{Lx}},{b = \frac{\left( {{mv}_{1}^{v} - {mv}_{0}^{v}} \right)}{Lx}},} & {{Equation}\mspace{14mu} 2.7{.3}} \\{{c = \frac{\left( {{mv}_{2}^{h} - {mv}_{0}^{h}} \right)}{Ly}},{d = \frac{\left( {{mv}_{2}^{v} - {mv}_{0}^{v}} \right)}{Ly}},} & {{Equation}\mspace{14mu} 2.7{.4}} \\{{{Lx} = {x_{1} - x_{0}}},{{Ly} - y_{2} - y_{0}},} & {{Equation}\mspace{14mu} 2.7{.5}}\end{matrix}$

where MV0 (mv₀ ^(h), mv₀ ^(v)), MV1 (mv₁ ^(h), mv₁ ^(v)) and MV2 (mv₂^(h), mv₂ ^(v)), represent three control point MVs (CPMVs) at position(x0, y0), (x1, y1) and (x2, y2), respectively. (x0, y0), (x1, y1) and(x2, y2) are typically set to be the top-left, top-right and bottom-leftcorner of an affine coded block with a size of w×h. Accordingly, Lx canbe set to be w and Ly can be set to be h.

It should be noted that the base MV is not necessary to be one of theCPMVs of an affine coded block, although it is set to be the CPMV MV0 atthe top-left corner (x0, y0) of an affine coded block in someembodiments.

7.2 Affine Inheritance Crossing CTU Rows

FIG. 14 shows a current CTU row (1430) and an above CTU row (1420) ontop of the current CTU row (1430). The current CTU row (1430) includes acurrent CTU (1404) under processing that includes an affine codedcurrent CU (1410). As shown, the current CU (1410) includes threecontrol points with coordinates (x0, y0), (x1, y1), and (x2, y2)corresponding to three CPMVs, MV_(C0), MV_(C1), and MV_(C2). The currentCU (1410) has a width of w.

The above CTU row (1420) includes CTUs (1401), (1402) and (1403), and aset of minimum blocks (or 4×4 blocks) denoted LL, B3, B2, N0, B0, B1,N1, R, R2, and RR. The CTU (1402) includes an affine coded neighboringCU (1411) of the current CU (1410).

In a first example, when an affine model of the current CU (1410) isinherited from a neighboring 4×4 block in the above CTU row (1420), MVsstored in a regular MV buffer are accessed. FIG. 14 shows an examplewhen the current CU (1410) applies affine merge mode, inheriting theaffine model from a neighboring block B0. In this case, a codec canstore the width of the CU (1411) covering B0 (Wn in FIG. 14), MVs of thebottom-left 4×4 block (N0) and bottom-right 4×4 block (N1) of the CU(1411) (MV_(N0) and MV_(N1) in FIG. 14), and a base position which isthe bottom-left coordinator (x_(N0), y_(N0)) of N0. In this example,MV_(N0) is used as a base MV.

In order to access MVs stored in a regular MV buffer, the width Wn andthe x-component of the bottom-left coordinate x_(N0) of the CU (1411)containing the 4×4 block can be stored for a 4×4 block at a line-buffer(e.g., B0). For example, for each 8-8 block, 3 bits for Wn and 5 bitsfor x_(N0) are required to be stored.

To reduce a size of line buffer, in a second example, a storage of a CUwidth and an x-component of a bottom-left coordinate of each 8×8 blockis removed from the line-buffer. When the current CU (1410) appliesaffine inheritance from a neighboring 4×4 block such as B0 in FIG. 14,the 4×4 block right-next to B0, or left-next to B0 which is alsoaffine-coded and has the same reference picture index as B0, is chosenas B0′. The regular MVs stored in B0 and B0′ are accessed as MVB andMVB′. MV0 and MV1 are set to be MVB and MVB′ to derive a and b byequation 2.7.3 with Lx=4. CPMVs of the current CU (1410) are derived byequation 2.7.1 with the center position of B0 as the base position andMVB as the base MV.

With the proposed method, at most 36 4×4 blocks from B3 to R2 as shownin FIG. 14 may be accessed at CTU-row boundary. The additionalinformation needs to be loaded on cache is reduced from 4464 bits to2*72=144 bits (or 2*10=20 bytes in a byte-alignment implementation).

7.3 Affine Inheritance Inside a CTU Row

In an example, when an affine model of a current CU is inherited from aneighboring 4×4 block in a current CTU row, CPMVs stored in a local CPMVbuffer (In-CTU-buffer) can be accessed. The current CU can inherit the4-parameter or the 6-parameter affine model from the neighboring CUbased on the CPMVs stored in the local buffer. For a 4×4 block inside aCTU, three CPMVs for two reference lists, the width, the height and thetop-left coordinate of a CU containing the 4×4 block can be stored.

To reduce a size of the local CPMV buffer, in another example, affineparameters instead of three CPMVs and the block dimensions are stored.When a current CU applies affine-inheritance merge mode, affineparameters are directly copied from a neighboring 4×4 block, denoted B,to be inherited. And a MV of each sub-block in the current CU isderived, for example, by equation 2.7.2 with a center position of B as abase position and regular MV at B as a base MV. When the current CUapplies affine AMVP mode, CPMVs of the current CU are derived byequation 2.7.2 also with the center position of B as the base positionand regular MV at B as the base MV, and the derived CPMVs will serve asthe motion vector predictors (MVPs).

In an example, each affine parameter is stored as an 8-bit signedinteger. So 2×4×8=64 bits can be stored for affine parameters in each8×8 block inside a CTU. With this method, the In-CTU-buffer is increasedby 48×64=3072 bits (or 48×8=384 bytes in a byte-alignmentimplementation) compared with storage of CPMVs). With the method, oneset of affine parameters are calculated at most only once compared withthe method of storage of CPMVs where the affine parameters may becalculated twice.

8. History-Based Affine Predication (Affine HMVP)

8.1 Affine HMVP Table

In some examples, an affine HMVP table storing affine motion candidatesis employed. After coding an affine coded current CU, motion informationof the current CU is used to update the affine HMVP table. Similar tothe regular HMVP table updating process, when adding a new motioncandidate to the affine HMVP table, a constrained FIFO rule is utilized.For example, a redundancy check is firstly applied to find whether thereis an identical affine HMVP candidate in the affine HMVP table. Iffound, the identical affine HMVP candidate is removed from the affineHMVP table. All the affine HMVP candidates afterwards are moved forward,i.e., with indices reduced by 1. In an example, a size of the affineHMVP table is set to 5 (five entries in the table), which is the same asa sub-block merge list size used in some embodiments. In an example, theHMVP table is reset at the beginning of a CTU row.

In an example, for each entry of the affine HMVP table, the followingmotion information is stored with a memory requirement listed:

Affine CPMVs mv0, mv1, mv2 for 2 reference lists (36 bits * 2 * 3)Reference index of List 0 and/or List1  (4 bits * 2) Inter predictiondirection (L0, L1 or Bi-pred)  (2 bits) Affine type, whether 4-parameteror 6-parameter affine  (1 bit) Position (x, y) (16 bits * 2) CU Widthand height  (5 bits * 2) Generalized bi-prediction index (GBI)(optional)  (3 bits) Total memory required: 136*2*3 + 4*2 + 2 + 1 +6*2 + 5*2 + 3 = 272 bits

Accordingly, memory requirements for affine HMVP tables of differencesizes are:

Table size of 1: 272 bits ˜34 bytes

Table size of 4: 1088 bits ˜136 bytes

Table size of 5: 1360 bits ˜170 bytes

8.2 Copying Affine CPMVs from an Affine HMVP Table

In an example, an affine HMVP candidate can be directly added to a mergecandidate list or an AMVP candidate list as an additional candidate. Forexample, the affine HMVP candidate can be added at a position afterconstructed affine candidates and before zero MV candidates. In anexample, there is no pruning check when adding an affine HMVP candidateto a merge list. In an example, CPMVs of an affine HMVP candidate are tobe applied to a current CU directly regardless of a correspondinghistory block's shape and size.

8.3 Affine Model Inheritance from an Affine HMVP Table

In an example, an affine model of an affine HMVP candidate is inheritedto generate an affine merge candidate or affine AMVP candidate. Similarto affine mode inheritance (or affine inheritance) from spatialneighbors, affine inheritance from an affine HMVP table uses a position,block width and/or height, and CPMVs stored in an affine HMVP buffer togenerate affine motion information.

8.3.1 Replacing Affine Inheritance from Spatial Neighbors withInheritance from an Affine HMVP Table

Inherited affine merge candidates and inherited affine AMVP candidatescan be derived from left and above neighboring blocks coded in affinemode. In an example, those affine candidates inherited from spatialneighbors are replaced with inherited candidates derived from an affineHMVP table. The affine merge and AMVP candidates inherited from theaffine HMVP can take the same positions as the replaced inherited affinecandidates. In an example, at most two inherited candidates from theaffine HMVP table are allowed in both affine merge mode and affine AMVPmode.

In an example, entries in the affine HMVP tables are checked startingfrom a latest entry. Only when an affine HMVP candidate neighbors acurrent CU, the affine HMVP candidate would be used to derive theinherited candidate. Whether an affine HMVP candidate is a neighbor ofthe current CU can be determined because position and size informationare stored in the affine HMVP table. For the affine HMVP candidate thatis identified as neighbors of the current CU, the width, height andCPMVs of this identified candidate are then used to derive CPMVs of thecurrent CU in the same way as affine inheritance from spatial neighbors.

8.3.2 Affine Inheritance from Affine H-MVP Table Combined with AffineInheritance from Above CTU Using Motion Data Line Buffer

In an example, in addition to the affine inheritance from an affine HMVPtable, as described in 8.3.1, affine inheritance from motion data linebuffer is also used for blocks located adjacent to the top boundary of acurrent CTU.

Affine motion data (or affine model) inheritance from above CTU isdescribed below. If a candidate CU for affine motion data inheritance isin an above CTU line (or row), regular MVs of a bottom-left andbottom-right sub-block (minimum block)(e.g., blocks with a size of 4×4pixels) in the line buffer instead of CPMVs are used for affine MVPderivation. In this way, no CPMVs corresponding to candidate CUs in theabove CTU row are stored, and only CPMVs of candidate CUs within acurrent CTU row are stored in a local buffer.

If the candidate CU in the above CTU row is coded with a 6-parameteraffine model, the affine model is degraded to a 4-parameter model forinheritance. Since the sub-block (minimum block) MVs represent themotion at the center of the respective sub-block, the distance of thetwo corner sub-block MVs at the bottom of the candidate CU is neiW-4pixels, wherein neiW is the width of the candidate CU. To avoid divisionby (neiW-4), which may not be power of 2, a rough distance neiW is usedfor the inheritance. The coordinates of bottom-left and bottom-rightcorner are set to (xNb, yNb+neiH) and (xNb+neiW, yNb+neiH) forinheritance, wherein neiH is the height of the candidate CU.

FIG. 15 shows an example of affine inheritance from an above CTU linebuffer. As shown, a first CTU row is above a CTU boundary (1511), and asecond CTU row is below the CTU boundary (1511). A current CTU is in thesecond CTU row and includes an affine coded current CU having CPMVs{right arrow over (ν₀)}, {right arrow over (ν₁)}, and {right arrow over(ν₂)} at control points (x0, y0), (x1, y1), and (x2, y2). The current CUhas neighboring CUs (or blocks) E, B, C, and D that are affine coded.The top-left and top-right corners of the block E have coordinates of(x_(E0), y_(E0)), and (x_(E1), y_(E1)), respectively. CPMVs {right arrowover (ν_(E0))}, {right arrow over (ν_(E1))}, {right arrow over(ν_(B0))}, {right arrow over (ν_(B1))}, {right arrow over (ν_(C0))},{right arrow over (ν_(C1))}, {right arrow over (ν_(D0))}, and {rightarrow over (ν_(D1))} corresponding to each of the blocks E, B, C, and Dare shown, and can be saved to a local buffer of the current CTU foraffine inheritance from spatial neighbors of the current CU.

Sub-block (minimum block) motion vectors indicated by dashed arrows(1502) and solid arrows (1503) are also shown. Those sub-block motionvectors correspond to minimum sub-blocks that have a minimum allowableblock size (typically 4×4 pixels). Motion information of each suchminimum block can be stored in a memory when an inter coded blockincluding the respective minimum blocks is processed and motioninformation of the inter coded block is available. The motioninformation corresponding to the minimum blocks, including therespective motion vectors indicated by arrows (1502) and (1503), can beused for everything, such as motion compensation (MC), merge/skip mode,AMVP mode, deblocking, and deriving of TMVPs. With respect to affinemotion information, the motion information corresponding to minimumblocks can be referred to as regular motion information.

In addition, the regular motion information of the minimum blocks abovethe CTU boundary (1511) can be stored in an above CTU row line buffer(1520), and used for affine inheritance for coding CUs within thecurrent CTU and adjacent to the CTU boundary (1511).

As an example, along the top CTU boundary (1511), the bottom-left andbottom right sub-block motion vectors of a CU are used for everythingand stored in the line buffer (1520). These sub-block MVs are also usedfor affine inheritance of neighboring affine CUs in bottom CTUs (CTUs inthe second row below the CTU boundary 1511). For example in CU E, thebottom-left and bottom right corner sub-block MVs {right arrow over(ν_(LE0))} and {right arrow over (ν_(LE1))} (marked in dashed arrows)are stored in the line buffer 1520, and used for affine inheritance. TheMVs {right arrow over (ν_(LE0))} and {right arrow over (ν_(LE1))} caneach start from a central position, (x_(LE0), y_(LE0)), or (x_(LE1),y_(LE1)), in the respective sub-block. In an example, the MVs {rightarrow over (ν_(LE0))} and {right arrow over (ν_(LE1))} can also be usedfor merge/skip/AMVP list derivation of neighboring CUs in bottom CTUsand for de-blocking.

As an example, based on the MVs {right arrow over (ν_(LE0))} and {rightarrow over (ν_(LE1))} at positions (x_(LE0), y_(LE0)), or (x_(LE1),y_(LE1)), respectively, the CPMVs {right arrow over (ν₀)}, and {rightarrow over (ν₁)} of the current CU can be derived by using the4-parameter model as follows,

$\begin{matrix}\left\{ \begin{matrix}\begin{matrix}{v_{0x} = {{\frac{\left( {v_{{LE}\; 1x} - v_{{LE}\; 0x}} \right)}{\left( {x_{{LE}\; 1} - x_{{LE}\; 0}} \right)}\left( {x_{0} - x_{{LE}\; 0}} \right)} -}} \\{{\frac{\left( {v_{{LE}\; 1y} - v_{{LE}\; 0y}} \right)}{\left( {x_{{LE}\; 1} - x_{{LE}\; 0}} \right)}\left( {y_{0} - y_{{LE}\; 0}} \right)} + v_{{LE}\; 0x}}\end{matrix} \\\begin{matrix}{v_{0y} = {{\frac{\left( {v_{{LE}\; 1y} - v_{{LE}\; 0y}} \right)}{\left( {x_{{LE}\; 1} - x_{{LE}\; 0}} \right)}\left( {x_{0} - x_{{LE}\; 0}} \right)} +}} \\{{\frac{\left( {v_{{LE}\; 1x} - v_{{LE}\; 0x}} \right)}{\left( {x_{{LE}\; 1} - x_{{LE}\; 0}} \right)}\left( {y_{0} - y_{{LE}\; 0}} \right)} + v_{{LE}\; 0y}}\end{matrix}\end{matrix} \right. & {{Equation}\mspace{14mu} 2.8{.1}} \\\left\{ \begin{matrix}\begin{matrix}{v_{1x} = {{\frac{\left( {v_{{LE}\; 1x} - v_{{LE}\; 0x}} \right)}{\left( {x_{{LE}\; 1} - x_{{LE}\; 0}} \right)}\left( {x_{1} - x_{{LE}\; 0}} \right)} -}} \\{{\frac{\left( {v_{{LE}\; 1y} - v_{{LE}\; 0y}} \right)}{\left( {x_{{LE}\; 1} - x_{{LE}\; 0}} \right)}\left( {y_{1} - y_{{LE}\; 0}} \right)} + v_{{LE}\; 0x}}\end{matrix} \\\begin{matrix}{v_{1y} = {{\frac{\left( {v_{{LE}\; 1y} - v_{{LE}\; 0y}} \right)}{\left( {x_{{LE}\; 1} - x_{{LE}\; 0}} \right)}\left( {x_{1} - x_{{LE}\; 0}} \right)} +}} \\{{\frac{\left( {v_{{LE}\; 1x} - v_{{LE}\; 0x}} \right)}{\left( {x_{{LE}\; 1} - x_{{LE}\; 0}} \right)}\left( {y_{1} - y_{{LE}\; 0}} \right)} + v_{{LE}\; 0y}}\end{matrix}\end{matrix} \right. & {{Equation}\mspace{14mu} 2.8{.2}}\end{matrix}$

And, if the current CU uses the 6-parameter affine motion model, thecontrol point vectors {right arrow over (ν₂)} can be derived by usingthe 4-parameter mode as follows,

$\begin{matrix}\left\{ \begin{matrix}\begin{matrix}{v_{2x} = {{\frac{\left( {v_{{LE}\; 1x} - v_{{LE}\; 0x}} \right)}{\left( {x_{{LE}\; 1} - x_{{LE}\; 0}} \right)}\left( {x_{2} - x_{{LE}\; 0}} \right)} -}} \\{{\frac{\left( {v_{{LE}\; 1y} - v_{{LE}\; 0y}} \right)}{\left( {x_{{LE}\; 1} - x_{{LE}\; 0}} \right)}\left( {y_{2} - y_{{LE}\; 0}} \right)} + v_{{LE}\; 0x}}\end{matrix} \\\begin{matrix}{v_{2y} = {{\frac{\left( {v_{{LE}\; 1y} - v_{{LE}\; 0y}} \right)}{\left( {x_{{LE}\; 1} - x_{{LE}\; 0}} \right)}\left( {x_{2} - x_{{LE}\; 0}} \right)} +}} \\{{\frac{\left( {v_{{LE}\; 1x} - v_{{LE}\; 0x}} \right)}{\left( {x_{{LE}\; 1} - x_{{LE}\; 0}} \right)}\left( {y_{2} - y_{{LE}\; 0}} \right)} + v_{{LE}\; 0y}}\end{matrix}\end{matrix} \right. & {{Equation}\mspace{14mu} 2.8{.3}}\end{matrix}$

In the above equations 2.8.1-2.8.3, the coordinates of the centralpositions corresponding to the MVs {right arrow over (ν_(LE0))} and{right arrow over (ν_(LE1))} are substituted with that of thebottom-lent and bottom-right corner of the CU E as follows,

$\begin{matrix}\left\{ \begin{matrix}{x_{{LE}\; 0} = x_{E\; 0}} \\{x_{{LE}\; 1} = x_{E\; 1}} \\{y_{{LE}\; 0} = y_{0}} \\{y_{{LE}\; 1} = y_{0}}\end{matrix} \right. & {{Equation}\mspace{14mu} 2.8{.4}}\end{matrix}$

As a result, a width of CU E is used in place of a distance between thepositions (x_(LE0), y_(LE0)) and (x_(LE1), y_(LE1)).

8.4 Affine HMVP Table with Affine Parameters Stored

In an example, an affine HMVP table is constructed in a way similar tothe methods described 8.1. However, instead of storing the affine CPMVvalues, affine parameters (e.g. the parameters a, b, c, or d inequations 2.7.3 and 2.7.4) are stored in each affine HMVP entry. Affineinheritance may be performed using the affine parameters from AffineHMVP to generate affine motion information for affine merge or affineAMVP candidates. In an example, history-based affine merge candidates(HAMC) are included into a sub-block based merge candidate list.

For example, after decoding an affine-coded CU, a set of affineparameters {a, b, c, d} for the two reference picture lists andassociated reference indices are put into an affine parameter historytable.

An HAMC can be derived by combining a set of affine parameters stored inthe table and a regular MV of a neighboring 4×4 block that serves as abase MV. For example, the MV of the current block at position (x, y) iscalculated as,

$\quad\left\{ \begin{matrix}{{{mv}^{h}\left( {x,y} \right)} = {{a\left( {x - x_{base}} \right)} + {c\left( {y - y_{base}} \right)} + {mv}_{base}^{h}}} \\{{{mv}^{v}\left( {x,y} \right)} = {{b\left( {x - x_{base}} \right)} + {d\left( {y - y_{base}} \right)} + {mv}_{base}^{v}}}\end{matrix} \right.$

where (mv^(h) _(base), mv^(v) _(base)) represents the MV of theneighboring 4×4 block, (x_(base), y_(base)) represents a center positionof the neighboring 4×4 block, and (x, y) can be the top-left, top-rightand bottom-left corner of the current block to obtain the CPMVs.

In an example, HAMCs derived from stored affine parameters and base MVsfrom spatial neighboring blocks are put into a sub-block based mergelist after a constructed affine merge candidate. For each set of storedaffine parameters in the HMVP table, a first valid neighboring 4×4 blockwith the same inter-prediction direction and reference indices as thoseassociated with the set of affine parameters is used to derive the HAMC.

In an example, HAMCs derived from stored affine parameters and base MVsfrom temporal neighboring block are put into a sub-block based beforezero candidate. For each set of stored affine parameters, the respectiveTMVP is scaled to the reference picture the parameters referring to, toderive the HAMC.

In an example, each affine model parameter can be stored as an 8-bitsigned integer. Up to 6 affine parameter sets are stored. Therefore, theaffine parameter history table can be small, and for example, has a sizeof 6×(8×4×2+8)=432 bits (42 bytes).

III. Other Affine Model Inheritance Techniques

As described, in order to save local memory used for processing a CTU,affine inheritance from neighboring blocks can be replaced with affineinheritance from an affine HMVP table. In addition, affine inheritancefrom minimum block motion information (or regular motion information)stored in an above CTU row line buffer can improve affine inheritanceperformance without the need for a local memory for affine CPMV storage.

To further improve affine motion based coding performance, other affinemodel inheritance techniques can be employed. For example, affineinheritance from regular motion information of neighboring blockslocated at a left CTU boundary can be employed. The affine inheritancefrom blocks above CTU (with regular motion information stored in a linebuffer) can further be improved.

1. Affine Inheritance from Regular Motion Information of Minimum Blocksin the Rightmost Column of a Left Neighboring CTU

In some embodiments, for an affine coded current block adjacent to theleft boundary of a current CTU, regular motion information of arightmost column of minimum blocks of a left neighboring CTU can be usedto derive an affine motion model for affine inheritance. For example,along the right CTU boundary of the left neighboring CTU, an affinecoded CU in the left neighboring CTU can be identified. The top-rightand bottom right sub-block (or minimum block) motion vectors of theidentified affine coded CU can be stored in a local buffer (or referredto as a left CTU boundary line buffer), and used for affine inheritanceof affine CUs in the current CTU as well as for other processingoperations (such as MC/merge mode/skip mode/AMVP mode/deblocking/TMVPdetermination processing, and the like).

In an example, the affine coded CU in the left neighboring CTU can beidentified by checking some predefined candidate positions along theleft boundary of the current CTU according to a predefined order. Forexample, those candidate positions can be represented by the minimumblocks of the rightmost column of minimum blocks of the left neighboringCTU.

Embodiment 1.1

In an embodiment, when a current block is located at the left edge of acurrent CTU, the current block's CPMVs can be determined based on anaffine motion model inherited from regular motion vectors stored in theright-most column of minimum blocks of a left neighboring CTU of thecurrent CTU. Subsequently, sub-block motion vectors of the current blockcan be derived from the current block's CPMVs.

FIG. 16 shows the same current CU as in FIG. 15 but with CU D at thetop-left corner and CU E at the bottom-left corner. Different from theFIG. 15 example, an affine merge or AMVP candidate can be derived fromregular motion information of a rightmost column of minimum blocks(1601) in the left CTU (1610) of the current CTU. For example, CU E inthe left CTU (1610) is affine coded. The top-left and bottom-leftcorners of CU E have coordinates of (x_(E0), y_(E0)), and (x_(E1),y_(E1)), respectively. The top-right and bottom right corner sub-blockof CU E have MVs {right arrow over (V_(LE0))} and {right arrow over(V_(LE1))} (marked in dashed arrows) that can be stored in a localbuffer for storing regular motion vectors of the left CTU. The MVs{right arrow over (V_(LE0))} and {right arrow over (V_(LE1))} can beused for the affine inheritance as well as deviation of amerge/skip/AMVP list or de-blocking of neighboring CUs in the currentCTU.

Based on the MVs {right arrow over (V_(LE0))} and {right arrow over(V_(LE0))}, the CPMVs {right arrow over (ν₀)} and {right arrow over(ν₁)} of the current CU can be derived as follows when a 4-parameteraffine model is used for the current block,

$\begin{matrix}\left\{ \begin{matrix}\begin{matrix}{v_{0x} = {{\frac{\left( {v_{{LE}\; 1x} - v_{{LE}\; 0x}} \right)}{\left( {y_{{LE}\; 1} - y_{{LE}\; 0}} \right)}\left( {x_{0} - x_{{LE}\; 0}} \right)} -}} \\{{\frac{\left( {v_{{LE}\; 1y} - v_{{LE}\; 0y}} \right)}{\left( {y_{{LE}\; 1} - y_{{LE}\; 0}} \right)}\left( {y_{0} - y_{{LE}\; 0}} \right)} + v_{{LE}\; 0x}}\end{matrix} \\\begin{matrix}{v_{0y} = {{\frac{\left( {v_{{LE}\; 1y} - v_{{LE}\; 0y}} \right)}{\left( {y_{{LE}\; 1} - y_{{LE}\; 0}} \right)}\left( {x_{0} - x_{{LE}\; 0}} \right)} +}} \\{{\frac{\left( {v_{{LE}\; 1x} - v_{{LE}\; 0x}} \right)}{\left( {y_{{LE}\; 1} - y_{{LE}\; 0}} \right)}\left( {y_{0} - y_{{LE}\; 0}} \right)} + v_{{LE}\; 0y}}\end{matrix}\end{matrix} \right. & {{Equation}\mspace{14mu} 3.1{.1}} \\\left\{ \begin{matrix}\begin{matrix}{v_{1x} = {{\frac{\left( {v_{{LE}\; 1x} - v_{{LE}\; 0x}} \right)}{\left( {y_{{LE}\; 1} - y_{{LE}\; 0}} \right)}\left( {x_{1} - x_{{LE}\; 0}} \right)} -}} \\{{\frac{\left( {v_{{LE}\; 1y} - v_{{LE}\; 0y}} \right)}{\left( {y_{{LE}\; 1} - y_{{LE}\; 0}} \right)}\left( {y_{1} - y_{{LE}\; 0}} \right)} + v_{{LE}\; 0x}}\end{matrix} \\\begin{matrix}{v_{1y} = {{\frac{\left( {v_{{LE}\; 1y} - v_{{LE}\; 0y}} \right)}{\left( {y_{{LE}\; 1} - y_{{LE}\; 0}} \right)}\left( {x_{1} - x_{{LE}\; 0}} \right)} +}} \\{{\frac{\left( {v_{{LE}\; 1x} - v_{{LE}\; 0x}} \right)}{\left( {y_{{LE}\; 1} - y_{{LE}\; 0}} \right)}\left( {y_{1} - y_{{LE}\; 0}} \right)} + v_{{LE}\; 0y}}\end{matrix}\end{matrix} \right. & {{Equation}\mspace{14mu} 3.1{.2}}\end{matrix}$

where ν_(LE0x), ν_(LE1x), ν_(0x), and ν_(1x) are horizontal componentsof the MVs {right arrow over (V_(LE0))}, {right arrow over (V_(LE1))},{right arrow over (ν₀)} and {right arrow over (ν₁)}, respectively, whileν_(LE0y), ν_(LE1y), ν_(0y), and ν_(1y) are vertical components of theMVs {right arrow over (V_(LE0))}, {right arrow over (V_(LE1))}, {rightarrow over (ν₀)} and {right arrow over (ν₁)}, respectively.

When a 6-parameter affine motion model is used for the current block,the CPMV {right arrow over (ν₂)} can be derived by

$\begin{matrix}\left\{ \begin{matrix}\begin{matrix}{v_{2x} = {{\frac{\left( {v_{{LE}\; 1x} - v_{{LE}\; 0x}} \right)}{\left( {y_{{LE}\; 1} - y_{{LE}\; 0}} \right)}\left( {x_{2} - x_{{LE}\; 0}} \right)} -}} \\{{\frac{\left( {v_{{LE}\; 1y} - v_{{LE}\; 0y}} \right)}{\left( {y_{{LE}\; 1} - y_{{LE}\; 0}} \right)}\left( {y_{2} - y_{{LE}\; 0}} \right)} + v_{{LE}\; 0x}}\end{matrix} \\\begin{matrix}{v_{2y} = {{\frac{\left( {v_{{LE}\; 1y} - v_{{LE}\; 0y}} \right)}{\left( {y_{{LE}\; 1} - y_{{LE}\; 0}} \right)}\left( {x_{2} - x_{{LE}\; 0}} \right)} +}} \\{{\frac{\left( {v_{{LE}\; 1x} - v_{{LE}\; 0x}} \right)}{\left( {y_{{LE}\; 1} - y_{{LE}\; 0}} \right)}\left( {y_{2} - y_{{LE}\; 0}} \right)} + v_{{LE}\; 0y}}\end{matrix}\end{matrix} \right. & {{Equation}\mspace{14mu} 3.1{.3}}\end{matrix}$

where ν_(2x) and ν_(2y) are horizontal and vertical components of theCPMV {right arrow over (ν₂)}.

In an example, the coordinates of positions of the MVs {right arrow over(V_(LE0))} and {right arrow over (V_(LE1))} at the top-right andbottom-right sub-blocks of CU E satisfy the following conditions:

$\begin{matrix}\left\{ \begin{matrix}{x_{{LE}\; 0} = x_{0}} \\{x_{{LE}\; 1} = x_{0}} \\{y_{{LE}\; 0} = y_{E\; 0}} \\{y_{{LE}\; 1} = y_{E\; 1}}\end{matrix} \right. & {{Equation}\mspace{14mu} 3.1{.4}}\end{matrix}$

Under the condition of equation 3.1.4, a height of CU E is used in placeof a distance between the positions (x_(LE0), y_(LE0)) and (x_(LE1),y_(LE1)) in FIG. 16. From another perspective, in the equations3.1.1-3.1.3, the MVs {right arrow over (V_(LE0))} and {right arrow over(V_(LE1))} are used as an approximation of CPMVs at the top-right andbottom-right corners of CU E.

Embodiment 1.2

In an embodiment, when a current block is located at the left edge of acurrent CTU, the current block's sub-block MVs are inherited fromregular motion vectors of a right-most column of minimum blocks of theleft neighboring CTU without deriving current block's CPMVs. The regularmotion vectors can be stored in a local buffer of the current CTU.

For example, in FIG. 16, based on the MVs {right arrow over (V_(LE0))}and {right arrow over (V_(LE1))}, for each sub-block of the current CUwith a center point located at coordinate (x_(s), y_(s)), an MV {rightarrow over (v_(s))} of the respective sub-block may be derived asfollows by using a 4-parameter model:

$\quad\left\{ \begin{matrix}\begin{matrix}{v_{sx} = {{\frac{\left( {v_{{LE}\; 1x} - v_{{LE}\; 0x}} \right)}{\left( {y_{{LE}\; 1} - y_{{LE}\; 0}} \right)}\left( {x_{s} - x_{{LE}\; 0}} \right)} -}} \\{{\frac{\left( {v_{{LE}\; 1y} - v_{{LE}\; 0y}} \right)}{\left( {y_{{LE}\; 1} - y_{{LE}\; 0}} \right)}\left( {y_{s} - y_{{LE}\; 0}} \right)} + v_{{LE}\; 0x}}\end{matrix} \\\begin{matrix}{v_{sy} = {{\frac{\left( {v_{{LE}\; 1y} - v_{{LE}\; 0y}} \right)}{\left( {y_{{LE}\; 1} - y_{{LE}\; 0}} \right)}\left( {x_{s} - x_{{LE}\; 0}} \right)} +}} \\{{\frac{\left( {v_{{LE}\; 1x} - v_{{LE}\; 0x}} \right)}{\left( {y_{{LE}\; 1} - y_{{LE}\; 0}} \right)}\left( {y_{s} - y_{{LE}\; 0}} \right)} + v_{{LE}\; 0y}}\end{matrix}\end{matrix} \right.$

where ν_(sx) and ν_(sy) represent horizontal and vertical components ofthe {right arrow over (v_(s))}.

For example, the regular MVs {right arrow over (V_(LE0))} and {rightarrow over (V_(LE1))} and a distance between the positions of theregular MVs or a height of CU E can be used as an affine merge or AMVPcandidate and stored in a merge or AMVP candidate list.

2. Affine Inheritance Based on Accurate Position Information

In some embodiments, regular motion information from an above CTU linebuffer and/or a right column of minimum blocks of a neighboring CTU withaccurate position information is used to derive an inherited affinecandidate.

For example, when deriving an affine model inheritance from regular MVsin a line buffer (above CTU), or a left CTU's right most column, insteadof using regular MVs of the sub blocks adjacent to control points as anapproximation of the CPMV values, the regular MVs with their precisepositions may be used for affine inheritance.

Embodiment 2.1

FIG. 17 shows a current block (1701) adjacent to a top CTU boundary(1711). The current block (1701) can have a height of H and a width ofW. A neighboring block (1702) of the current block (1701) is identifiedin a CTU above the CTU boundary (1711), for example, by checking acandidate position (1731). The neighboring block (1702) can have a widthof W′. A sequence of minimum blocks (e.g., having a size of 4×4 pixels)in an above CTU row (1721) each have regular motion information storedin an above CTU line buffer (1720). In an embodiment, the current block(1701)'s sub-block motion vectors may be derived from regular MVs of theminimum blocks in the neighboring block (1702) using affine inheritancewith a 4-parameter affine model.

In an example, a set of affine related information, such as an affineflag, the block width (W′), and a block position (e.g., a horizontalcoordinate of a bottom-left corner of the neighboring block (1702)), canbe associated with the candidate position (1731) and stored in a localbuffer or the line buffer (1720). The affine flag can indicate theneighboring block (1702) is affine coded. The block width and the blockposition together can be used to determine number and positions of eachminimum blocks of the neighboring block (1702) along the CTU boundary(1711). By checking the candidate position (1731), the set of affinerelated information can be obtained.

Based on regular motion information of any two of the minimum blocks ofthe neighboring block (1702) along the CTU boundary (1711), a4-parameter affine motion model can be determined and used for theaffine inheritance from the above CTU row (1721).

For example, the following two minimum blocks can be selected for affineinheritance: (i) the minimum block (1731) having a regular MV {rightarrow over (v₀)} at a central position (x₀, y₀), and (ii) a minimumblock (1732) having a regular MV {right arrow over (v₁)} at a centralposition (x₁, y₁). Based on the selected two minimum blocks (1731) and(1732), and the accurate positions (x₀, y₀) and (x₁, y₁), a MV {rightarrow over (v_(s))} at a central position (x, y) of a sub-block of thecurrent block (1701) can be derived as follows.

$\begin{matrix}\left\{ \begin{matrix}{v_{sx} = {{\frac{\left( {v_{1x} - v_{0x}} \right)}{\left( {x_{1} - x_{0}} \right)}\left( {x - x_{0}} \right)} -}} \\{{\frac{\left( {v_{1y} - v_{0y}} \right)}{\left( {x_{1} - x_{0}} \right)}\left( {y - y_{0}} \right)} + v_{0x}} \\\begin{matrix}{v_{sy} = {{\frac{\left( {v_{1y} - v_{0y}} \right)}{\left( {x_{1} - x_{0}} \right)}\left( {x - x_{0}} \right)} +}} \\{{\frac{\left( {v_{1x} - v_{0x}} \right)}{\left( {x_{1} - x_{0}} \right)}\left( {y - y_{0}} \right)} + v_{0y}}\end{matrix}\end{matrix} \right. & {{Equation}\mspace{14mu} 3.2{.1}}\end{matrix}$

In an example, a distance, x₁-x₀, between the positions (x₀, y₀) and(x₁, y₁) is restricted to be a power of 2 when the two minimum blocks(1731) and (1732) are being selected. Under such a configuration, thedivision operations in equation 3.2.1 can be implemented with shiftingoperations to reduce computational cost.

In an example, the selected minimum block (1731) is the minimum blockadjacent to the bottom-left corner, and the minimum block (1732) isselected to be a bottom-middle sub-block with a horizontal displacementof W′/2 to the sub-block (1731). In this way, the distance, x₁-x₀,between the positions (x₀, y₀) and (x₁, y₁) is restricted to be a halfof the width of the neighboring block (1702) that is typically a powerof 2.

In an example, CPMVs of the current block 1701 are derived basedequation 3.2.1, and used as a merge or AMVP candidate. In anotherexample, the regular MVs {right arrow over (v₀)} and {right arrow over(v₁)} and the distance between the two MVs are used as a merge or AMVPcandidate and added to a merge or AMVP candidate list.

Embodiment 2.2

FIG. 18 shows a current block (1801) adjacent to a left CTU boundary(1811). The current block (1801) can have a height of H and a width ofW. A neighboring block (1802) of the current block (1801) is identifiedin a CTU to the left of the CTU boundary (1811), for example, bychecking a candidate position (1834). The neighboring block (1802) canhave a height of H′. A sequence of minimum blocks (e.g., having a sizeof 4×4 pixels) in a right most column (1821) of a CTU neighboring thecurrent block (1801) each have regular motion information stored in alocal buffer (1820). In an embodiment, the current block (1801)'ssub-block motion vectors may be derived from regular MVs of the minimumblocks in the neighboring block (1802) using affine inheritance with a4-parameter affine model.

Similarly, a set of affine related information, such as an affine flag,the block height (H′), and a block position (e.g., a vertical coordinateof a bottom-right corner of the neighboring block (1802)), can beassociated with the candidate position (1834) and stored in the linebuffer (1820).

Based on regular motion information of any two of the minimum blocks ofthe neighboring block (1802) along the CTU boundary (1811), a4-parameter affine motion model can be determined and used for theaffine inheritance from the right-most column (1821).

For example, the following two minimum blocks can be selected for affineinheritance: (i) the minimum block (1831) having a regular MV {rightarrow over (v₀)} at a central position (x₀, y₀), and (ii) a minimumblock (1832) having a regular MV {right arrow over (v₁)} at a centralposition (x₁, y₁). Based on the selected two minimum blocks (1831) and(1832), and the accurate positions (x₀, y₀) and (x₁, y₁), a MV {rightarrow over (v_(s))} at a central position (x, y) of a sub-block of thecurrent block (1801) can be derived as follows,

$\begin{matrix}\left\{ \begin{matrix}{v_{sx} = {{\frac{\left( {v_{1x} - v_{0x}} \right)}{\left( {y_{1} - y_{0}} \right)}\left( {x - x_{0}} \right)} -}} \\{{\frac{\left( {v_{1y} - v_{0y}} \right)}{\left( {y_{1} - y_{0}} \right)}\left( {y - y_{0}} \right)} + v_{0x}} \\\begin{matrix}{v_{sy} = {{\frac{\left( {v_{1y} - v_{0y}} \right)}{\left( {x_{1} - x_{0}} \right)}\left( {x - x_{0}} \right)} +}} \\{{\frac{\left( {v_{1x} - v_{0x}} \right)}{\left( {y_{1} - y_{0}} \right)}\left( {y - y_{0}} \right)} + v_{0y}}\end{matrix}\end{matrix} \right. & {{Equation}\mspace{14mu} 3.2{.2}}\end{matrix}$

Similarly, a distance, y₁-y₀, between the positions (x₀, y₀) and (x₁,y₁) can be restricted to be a power of 2. Under such a configuration,the division operations in equation 3.2.2 can be implemented withshifting operations to reduce computational cost.

In an example, the selected minimum block (1831) is the minimum blockadjacent to the top-right corner, and the minimum block (1832) isselected to be a right-middle sub-block with a horizontal displacementof H′/2 to the sub-block (1831). In this way, the distance, y₁-y₀,between the positions (x₀, y₀) and (x₁, y₁) is restricted to be a halfof the height of the neighboring block (1802) that is typically a powerof 2.

Embodiment 2.3

Depending on a location of a current block, the methods as described inthe embodiment 2.1 and/or 2.2 can be used to determine one or moreinherited affine merge candidates. For example, when the current blockis adjacent to a top CTU boundary, the methods of embodiment 2.1 can beemployed. When the current block is adjacent to a left CTU boundary, themethods of embodiment 2.2 can be employed. When the current block isadjacent to a top-left corner of a CTU, the methods of both theembodiments 2.1 and 2.2 can be employed.

In an example, a checking at candidate positions for availability ofaffine coded blocks neighboring a current block can be performed in away similar to the methods described in the section II.2 based on FIG.8. In an example, the availability checking for affine coded blocks canbe performed using neighboring positions of a current block (1901)depicted in FIG. 19 in any predefined orders.

Taking FIG. 19 as an example, when the current block (1901) is adjacentto a top CTU boundary, the availability checking for affine codedneighboring blocks above the top CTU boundary can be performed over thepositions B2, B3, B1, and B0 in a predefined order. When the currentblock (1901) is adjacent to a left CTU boundary, the availabilitychecking for affine coded neighboring blocks adjacent to the left CTUboundary can be performed over the positions A0, A1, and A2 in apredefined order. When the current block (1901) is adjacent to atop-left corner of a current CTU, the availability checking for affinecoded blocks can be performed over the positions A0, A1, A2, B2, B3, B1,and B0 in a predefined order.

In other examples, the set of positions for checking affine coded blockavailability can be defined differently from that in FIG. 8 or 19examples.

3. Combination of Affine Inheritance Sources

Affine inheritance sources can include (i) an affine HMVP table, (ii)regular MVs (or regular motion information) of sub-blocks (minimumblocks) of affine neighboring blocks above a CTU boundary, (iii) regularMVs of sub-blocks of affine neighboring blocks on the left of a CTUboundary, or (iv) spatial neighboring affine blocks (e.g., affine motioninformation in the form of CPMVs or affine model parameters). In variousembodiments, different affine inheritance sources can be employed forencoding or decoding a current block in a current CTU.

Embodiment 3.1

In an embodiment, affine inheritance is performed from an affine HMVPtable. Affine inheritance from spatial neighboring affine blocks orregular MVs of affine neighboring blocks is not used.

Embodiment 3.2

In an embodiment, when spatial neighbors of the current block arelocated within the current CTU, affine inheritance from the spatialneighbors may be replace by affine inheritance from an affine HMVPtable.

For example, the current block is not adjacent to a top, a left, or bothboundaries of a current CTU. No affine inheritance from spatialneighbors is performed. Instead, affine inheritance from the affine HMVPtable is used.

Embodiment 3.3

In another embodiment, when the current block is located adjacent to thetop boundary of the current CTU, affine inheritance from the currentblock's left neighboring blocks may be replaced by affine inheritancefrom an affine HMVP table. Affine inheritance from the current block'sabove neighboring blocks may be replaced by affine inheritance fromregular MVs of the neighboring affine blocks stored in an above CTUmotion data line buffer.

An order of affine inheritance from the affine inheritance sources canbe:

a. the affine HMVP table→regular MVs from the above CTU boundary; or

b. regular MVs from the above CTU boundary→the affine HMVP table.

For example, when inherited affine merge candidates on a merge candidatelist for processing the current block is limited to a maximum allowednumber N, affine candidate availability checking can be performedaccording to the order of a or b. The first N available affinecandidates can be selected to be included in the merge candidate list.

Embodiment 3.4

In another embodiment, when the current block is located adjacent to theleft boundary of the current CTU, the affine inheritance from its aboveneighboring blocks may be replaced by affine inheritance from an affineHMVP table; and the affine inheritance from its left neighboring blocksmay be replaced by inheritance from regular MVs of a neighboring affineblock stored in a local MV buffer corresponding to a left CTUneighboring the current CTU.

An order of affine inheritance from the affine inheritance sources canbe:

a. the affine HMVP table→regular MVs from the left CTU boundary; or

b. regular MVs from the left CTU boundary→the affine HMVP table.

Embodiment 3.5

In another embodiment, when the current block is located adjacent to thetop-left corner of the current CTU, the affine inheritance from thecurrent block's left neighboring blocks may be replaced by affineinheritance from an affine HMVP table; and the affine inheritance fromthe current block's above neighboring blocks may be replaced byinheritance from regular MVs of the neighboring affine block stored inan above CTU motion data line buffer.

An order of affine inheritance from the affine inheritance sources canbe:

a. an affine HMVP table→regular MVs from the above CTU boundary; or

b. regular MVs from the above CTU boundary→the Affine HMVP table.

Embodiment 3.6

In another embodiment, when the current block is located adjacent to thetop-left corner of the current CTU, the affine inheritance from thecurrent block's above neighboring blocks may be replaced by affineinheritance from an affine HMVP table; and the affine inheritance fromthe current block's left neighboring blocks may be replaced byinheritance from regular MVs of a neighboring affine block stored in alocal MV buffer corresponding to the left CTU.

An order of affine inheritance from the affine inheritance sources canbe:

a. the affine HMVP table→regular MVs from the left CTU boundary; or

b. regular MVs from the left CTU boundary→the affine HMVP table.

Embodiment 3.7

In another embodiment, when the current block is located adjacent to thetop-left corner of the current CTU, the affine inheritance from thecurrent block's left neighboring blocks may be replaced by affineinheritance from regular MVs of a neighboring affine block stored in alocal MV buffer corresponding to the left CTU; and the affineinheritance from the current block's above neighboring blocks may bereplaced by inheritance from regular MVs of a neighboring affine blockstored in an above CTU motion data line buffer.

An order of affine inheritance from the affine inheritance sources canbe:

a. regular MVs from the left CTU boundary→regular MVs from above CTUboundary; or

b. regular MVs from the above CTU boundary→regular MVs from the left CTUboundary.

When more than 2 inherited affine merge candidates are allowed,inheritance from an affine HMVP table may be used as additionalcandidates to affine merge candidates inherited from the left or theabove CTU boundary. In such case, an order of affine inheritance fromthe affine inheritance sources can be:

-   -   a. regular MVs from the left CTU boundary→regular MVs from the        above CTU boundary→an affine HMVP table;    -   b. regular MVs from the above CTU boundary→regular MVs from the        left CTU boundary→an affine HMVP table;    -   c. an affine HMVP table→regular MVs from the above CTU        boundary→regular MVs from the left CTU boundary;    -   d. an affine HMVP table→regular MVs from the left CTU        boundary→regular MVs from the above CTU boundary;    -   e. regular MVs from the above CTU boundary→an affine HMVP        table→regular MVs from the left CTU boundary.    -   f. regular MVs from the left CTU boundary→an affine HMVP        table→regular MVs from the above CTU boundary.

Embodiment 3.8

In another embodiment, when the current block is located adjacent to thetop-left corner of the current CTU, availability of neighboring affineblocks may be checked in a predefined order, and inherited affine mergecandidates of the current block may be derived from regular MVscorresponding to the first N available neighboring affine blocks.

In various examples, the checked positions can be the positions shown inFIG. 19, {A0, A1, A2, B0, B1, B2, B3}, or any subset of the depictedpositions. An order of availability checking may be one of anypredefined orders.

4. Number of Inherited Merge Candidates to be Used in Affine Inheritance

In an example, up to 2 affine inheritances are used for affine mergecandidates and/or affine AMVP candidates. For example, a sub-block basedmerge candidate list can be constructed for processing a current block.The sub-block based merge candidate list can include a number ofsub-block based TMVP (SubTMVP) merge candidates, and a number ofinherited affine merge candidates, followed by a number of constructedaffine merge candidates. When the number of the available mergecandidates is smaller than a maximum allowed number, the sub-block basedmerge candidate list can be filled with zero candidates. The number ofinherited affine merge candidates can be configured to be 2, or have adefault number of two.

In an example, such as the example of the section II.8.3.2, when acurrent block is not adjacent to a current CTU top boundary, up to twoinheritances from an affine HMVP table are allowed; and when the currentblock is located at the top of the current CTU (adjacent to CTU topboundary), one inheritance is allowed to be from above CTU (from regularMVs stored in an above CTU line buffer), and the other inheritance isallowed to be from the affine HMVP table. If there's no affinecandidates above CTU and/or no valid affine candidates in the affineHMVP table, the number of inheritances used may be less than 2.

In some embodiments, to further improve coding efficiency, more affineinheritances may be allowed for determining inherited affine mergecandidates in affine merge or affine AMVP.

Embodiment 4.1

In one embodiment, up to M affine inheritances from an affine HMVP tableare always allowed. If a current block is at the top of a CTU boundary,up to N inheritances from regular MVs of an above CTU are also allowedas additional inherited affine merge candidates.

In one example, M is equal to 2, and N is equal to 1. The values of Mand/or N may be other integer values, and are not limited by thisexample.

The valid inherited candidates may be added to an affine merge list(e.g., a merge list including affine merge candidates) or an affine AMVPcandidate list (e.g., an AMVP candidate list including affine AMVPcandidates) in any configured or predefined order.

Embodiment 4.2

In another embodiment, up to M affine inheritances from an affine HMVPtable are always allowed. If a current block is at the left of a CTUboundary, up to N inheritances from regular MVs of a left CTU is alsoallowed as additional candidates.

In one example, M is equal to 2, and N is equal to 1. The values of Mand/or N may be other integer values, and are not limited by thisexample.

The valid inherited candidates may be added to an affine merge list oran affine AMVP candidate list in any order.

Embodiment 4.3

In another embodiment, up to M affine inheritances from an affine HMVPtable are always allowed. If a current block is at the top-left cornerof a current CTU, up to N inheritances from a left CTU are also allowedas additional affine merge candidates, and up to K inheritances from anabove CTU are also allowed as additional candidates.

In one example, M is equal to 2, N is equal to 1, and K is equal to 1.The values of M, N, or K may be other integer values, and are notlimited by this example.

The valid inherited candidates may be added to an affine merge list oran affine AMVP candidate list in any order.

5. Affine HMVP Table Storing Affine Parameters

In some examples, affine inheritance from an affine HMVP table is usedto replace affine inheritance from spatial neighboring affine blocks, asdescribed in the section II.8.3.1 and II.8.3.2. This affine inheritancefrom an affine HMVP table may be based on different affine HMVP tableimplementations.

Embodiment 5.1

In an embodiment, when an affine HMVP table is implemented using themethod as described in the section II.2.8.4, inherited affine mergecandidates on a merge or AMVP list from spatial neighboring blocks maybe replaced by affine candidates from the affine HMVP table with affineparameters stored. For example, the affine merge candidates can take theform of affine parameters (e.g., the affine parameter a, b, c, or d inequations 2.7.3 and 2.7.4) instead of CPMVs.

6. An Example Process of Affine Model Inheritance

FIG. 20 shows a flow chart outlining a process (2000) according to someembodiments of the disclosure. The process (2000) can be used fordecoding an affine coded block. In various embodiments, the process(2000) are executed by processing circuitry, such as the processingcircuitry in the terminal devices (210), (220), (230) and (240), theprocessing circuitry that performs functions of the video decoder (310),the processing circuitry that performs functions of the video decoder(410), and the like. In some embodiments, the process (2000) isimplemented in software instructions, thus when the processing circuitryexecutes the software instructions, the processing circuitry performsthe process (2000). The process starts at (S2001) and proceeds to(S2010).

At S2010, an affine coded current block in a current CTU is received.The current block can be encoded with an AMVP mode or a merge mode.

At S2020, a position of the current block within the current CTU isdetermined based on coordinate information associated with the currentblock.

At S2030, when the current block is on a left boundary of the currentCTU, a four parameter affine model can be inherited from regular motioninformation in a left neighboring CTU of the current CTU. For example, amerge or AMVP candidate list can be constructed to decode the currentblock. The inherited affine model can be used to determine an affinecandidate on the merge or AMVP candidate list. For example, CPMVs of thecurrent block or affine model parameters can be determined based on theregular motion information, and stored as the affine candidate.

For example, the four parameter affine model can be determined based onregular motion information of two minimum blocks in a rightmost columnof minimum blocks of the left neighboring CTU. That regular motioninformation can be retrieved from a local memory for decoding thecurrent CTU. Either an approximated distance or an accurate distancebetween respective regular MVs can be used in different embodiments.

In some examples, an additional merge or AMVP candidate can be inheritedfrom an HMVP table in addition to the one inherited from the leftneighboring CTU.

At S2040, when the current block is on a top boundary of the currentCTU, a four parameter affine model can be inherited from regular motioninformation in a CTU row above the current CTU. Similarly, the inheritedaffine model can be used to determine an affine candidate on the mergeor AMVP candidate list. For example, CPMVs of the current block oraffine model parameters can be determined based on the regular motioninformation, and stored as the affine candidate.

For example, the four parameter affine model can be determined based onregular motion information of two minimum blocks from a bottom row ofminimum blocks in the CTU row above the current CTU row. That regularmotion information can be retrieved from an above CTU row line buffer.

In some examples, an additional merge or AMVP candidate can be inheritedfrom an HMVP table in addition to the one inherited from the CTU rowabove the current CTU.

At S2050, when the current block is adjacent to a top-left corner of thecurrent CTU, two four parameter affine models can be inherited based onregular motion information from the left neighboring CTU and the CTU rowabove the current CTU, respectively.

In some example, more than two inherited affine candidate are allowed.An additional inherited affine candidate can be from an HMVP table.

At S2060, when the current block is not adjacent to the top or leftboundary of the current CTU, one or more affine candidates can beinherited from an HMVP table. In some examples, inheritance from regularmotion information from neighboring CTUs is not used.

Following each of S2030-S2060, the process 2000 may proceed to S2099,and terminate at S2099.

IV. Computer System

The techniques described above, can be implemented as computer softwareusing computer-readable instructions and physically stored in one ormore computer-readable media. For example, FIG. 21 shows a computersystem (2100) suitable for implementing certain embodiments of thedisclosed subject matter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by one or more computer central processingunits (CPUs), Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 21 for computer system (2100) are exemplaryin nature and are not intended to suggest any limitation as to the scopeof use or functionality of the computer software implementingembodiments of the present disclosure. Neither should the configurationof components be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in theexemplary embodiment of a computer system (2100).

Computer system (2100) may include certain human interface inputdevices. Such a human interface input device may be responsive to inputby one or more human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard (2101), mouse (2102), trackpad (2103), touchscreen (2110), data-glove (not shown), joystick (2105), microphone(2106), scanner (2107), camera (2108).

Computer system (2100) may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen (2110), data-glove (not shown), or joystick (2105), butthere can also be tactile feedback devices that do not serve as inputdevices), audio output devices (such as: speakers (2109), headphones(not depicted)), visual output devices (such as screens (2110) toinclude CRT screens, LCD screens, plasma screens, OLED screens, eachwith or without touch-screen input capability, each with or withouttactile feedback capability—some of which may be capable to output twodimensional visual output or more than three dimensional output throughmeans such as stereographic output; virtual-reality glasses (notdepicted), holographic displays and smoke tanks (not depicted)), andprinters (not depicted).

Computer system (2100) can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW(2120) with CD/DVD or the like media (2121), thumb-drive (2122),removable hard drive or solid state drive (2123), legacy magnetic mediasuch as tape and floppy disc (not depicted), specialized ROM/ASIC/PLDbased devices such as security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system (2100) can also include an interface to one or morecommunication networks. Networks can for example be wireless, wireline,optical. Networks can further be local, wide-area, metropolitan,vehicular and industrial, real-time, delay-tolerant, and so on. Examplesof networks include local area networks such as Ethernet, wireless LANs,cellular networks to include GSM, 3G, 4G, 5G, LTE and the like, TVwireline or wireless wide area digital networks to include cable TV,satellite TV, and terrestrial broadcast TV, vehicular and industrial toinclude CANBus, and so forth. Certain networks commonly require externalnetwork interface adapters that attached to certain general purpose dataports or peripheral buses (2149) (such as, for example USB ports of thecomputer system (2100)); others are commonly integrated into the core ofthe computer system (2100) by attachment to a system bus as describedbelow (for example Ethernet interface into a PC computer system orcellular network interface into a smartphone computer system). Using anyof these networks, computer system (2100) can communicate with otherentities. Such communication can be uni-directional, receive only (forexample, broadcast TV), uni-directional send-only (for example CANbus tocertain CANbus devices), or bi-directional, for example to othercomputer systems using local or wide area digital networks. Certainprotocols and protocol stacks can be used on each of those networks andnetwork interfaces as described above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core (2140) of thecomputer system (2100).

The core (2140) can include one or more Central Processing Units (CPU)(2141), Graphics Processing Units (GPU) (2142), specialized programmableprocessing units in the form of Field Programmable Gate Areas (FPGA)(2143), hardware accelerators for certain tasks (2144), and so forth.These devices, along with Read-only memory (ROM) (2145), Random-accessmemory (2146), internal mass storage such as internal non-useraccessible hard drives, SSDs, and the like (2147), may be connectedthrough a system bus (2148). In some computer systems, the system bus(2148) can be accessible in the form of one or more physical plugs toenable extensions by additional CPUs, GPU, and the like. The peripheraldevices can be attached either directly to the core's system bus (2148),or through a peripheral bus (2149). Architectures for a peripheral businclude PCI, USB, and the like.

CPUs (2141), GPUs (2142), FPGAs (2143), and accelerators (2144) canexecute certain instructions that, in combination, can make up theaforementioned computer code. That computer code can be stored in ROM(2145) or RAM (2146). Transitional data can be also be stored in RAM(2146), whereas permanent data can be stored for example, in theinternal mass storage (2147). Fast storage and retrieve to any of thememory devices can be enabled through the use of cache memory, that canbe closely associated with one or more CPU (2141), GPU (2142), massstorage (2147), ROM (2145), RAM (2146), and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind wellknown and available to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system havingarchitecture (2100), and specifically the core (2140) can providefunctionality as a result of processor(s) (including CPUs, GPUs, FPGA,accelerators, and the like) executing software embodied in one or moretangible, computer-readable media. Such computer-readable media can bemedia associated with user-accessible mass storage as introduced above,as well as certain storage of the core (2140) that are of non-transitorynature, such as core-internal mass storage (2147) or ROM (2145). Thesoftware implementing various embodiments of the present disclosure canbe stored in such devices and executed by core (2140). Acomputer-readable medium can include one or more memory devices orchips, according to particular needs. The software can cause the core(2140) and specifically the processors therein (including CPU, GPU,FPGA, and the like) to execute particular processes or particular partsof particular processes described herein, including defining datastructures stored in RAM (2146) and modifying such data structuresaccording to the processes defined by the software. In addition or as analternative, the computer system can provide functionality as a resultof logic hardwired or otherwise embodied in a circuit (for example:accelerator (2144)), which can operate in place of or together withsoftware to execute particular processes or particular parts ofparticular processes described herein. Reference to software canencompass logic, and vice versa, where appropriate. Reference to acomputer-readable media can encompass a circuit (such as an integratedcircuit (IC)) storing software for execution, a circuit embodying logicfor execution, or both, where appropriate. The present disclosureencompasses any suitable combination of hardware and software.

APPENDIX A: ACRONYMS

-   AMVP: Advanced Motion Vector Prediction-   ASIC: Application-Specific Integrated Circuit-   BMS: benchmark set-   CANBus: Controller Area Network Bus-   CD: Compact Disc-   CPMV: Control Point Motion Vector-   CPUs: Central Processing Units-   CRT: Cathode Ray Tube-   CTUs: Coding Tree Units-   CU: Coding Unit-   DVD: Digital Video Disc-   FPGA: Field Programmable Gate Areas-   GBi: Generalized Bi-prediction-   GOPs: Groups of Pictures-   GPUs: Graphics Processing Units-   GSM: Global System for Mobile communications-   HEVC: High Efficiency Video Coding-   HMVP: History-based Motion Vector Prediction-   HRD: Hypothetical Reference Decoder-   IC: Integrated Circuit-   JEM: joint exploration model-   LAN: Local Area Network-   LCD: Liquid-Crystal Display-   LTE: Long-Term Evolution-   MMVD: Merge with MVD-   MV: Motion Vector-   MVD: Motion Vector Difference-   MVP: Motion Vector Predictor-   OLED: Organic Light-Emitting Diode-   PBs: Prediction Blocks-   PCI: Peripheral Component Interconnect-   PLD: Programmable Logic Device-   PUs: Prediction Units-   RAM: Random Access Memory-   ROM: Read-Only Memory-   SEI: Supplementary Enhancement Information-   SNR: Signal Noise Ratio-   SSD: solid-state drive-   SPS: Sequence Parameter Set-   sbTMVP: subblock-based temporal motion vector prediction-   TMVP: Temporal Motion Vector Prediction-   TUs: Transform Units,-   USB: Universal Serial Bus-   VUI: Video Usability Information-   VVC: versatile video coding

While this disclosure has described several exemplary embodiments, thereare alterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods which, although not explicitly shown or described herein,embody the principles of the disclosure and are thus within the spiritand scope thereof.

What is claimed is:
 1. A method of video decoding at a video decoder,comprising: receiving a current block that is affine coded and includedin a current coding tree unit (CTU); in response to a determination thatthe current block is adjacent to a top-left corner, a left boundary, ora top boundary of the current CTU, checking an availability of affinecoded blocks that are outside the current CTU and neighbor the currentblock at predefined candidate positions according to a predefined order;determining an affine model based on regular motion information ofminimum sized blocks corresponding to first N available affine codedblocks determined from the checking, N being an integer greater thanzero; and determining a first inherited affine candidate based on thedetermined affine model.
 2. The method of claim 1, wherein thedetermining the first inherited affine candidate includes: determiningcontrol point motion vectors (CPMVs) of the current block based on thedetermined affine model; and determining the first inherited affinecandidate based on the determined CPMVs.
 3. The method of claim 1,further comprising: determining sub-block motion vectors (MVs) of thecurrent block based on the regular motion information of the minimumsized blocks without deriving control point motion vectors (CPMVs) ofthe current block.
 4. The method of claim 1, wherein the determinedaffine model is a four parameter affine model determined by using MVs ofthe minimum sized blocks that are adjacent to control points of anaffine coded left neighboring block of the current block as anapproximation of control point motion vectors (CPMVs) at the controlpoints of the affine coded left neighboring block, and wherein the firstinherited affine candidate is determined based on the four parameteraffine model.
 5. The method of claim 1, wherein the determined affinemodel is a four parameter affine model determined by using precisepositions of MVs of the minimum sized blocks that are within an affinecoded left neighboring block of the current block, and wherein the firstinherited affine candidate is determined based on the four parameteraffine model.
 6. The method of claim 5, wherein a distance between theprecise positions of the MVs of the minimum sized blocks is a power oftwo.
 7. The method of claim 5, wherein a first one of the minimum sizedblocks is adjacent to a control point of the affine coded leftneighboring block, and a distance between the precise positions of twoMVs of the minimum sized blocks is a half of a height of the affinecoded left neighboring block.
 8. The method of claim 1, furthercomprising: including an inherited affine candidate from a history-basedmotion vector prediction (HMVP) table in a merge candidate list or anadvanced motion vector prediction (AMVP) candidate list that includes atmost two inherited affine candidates.
 9. The method of claim 1, furthercomprising: determining a second affine model based on second regularmotion information of two second minimum sized blocks in a bottom row ofminimum sized blocks above a CTU row including the current CTU inresponse to a determination that the current block is adjacent to a topboundary of the current CTU; and determining a second inherited affinecandidate based on the determined second affine model.
 10. The method ofclaim 9, wherein the determined second affine model is a four parameteraffine model determined by using precise positions of two MVs of the twosecond minimum sized blocks that are within an affine coded topneighboring block of the current block, and wherein the second inheritedaffine candidate is determined based on the four parameter affine model.11. The method of claim 10, wherein a distance between the precisepositions of the two MVs of the two second minimum sized blocks is apower of two.
 12. The method of claim 10, wherein a first one of the twosecond minimum sized blocks is adjacent to a control point of the affinecoded top neighboring block, and a distance between the precisepositions of the two MVs of the two second minimum sized blocks is ahalf of a width of the affine coded top neighboring block.
 13. Themethod of claim 9, further comprising: in response to a determinationthat the current block is adjacent to the top boundary of the currentCTU, including an inherited affine candidate from a history-based motionvector prediction (HMVP) table in a merge candidate list or an advancedmotion vector prediction (AMVP) candidate list that includes at most twoinherited affine candidates.
 14. The method of claim 1, furthercomprising: in response to a determination that the current block is notadjacent to a left or a top boundary of the current CTU, determining aninherited affine candidate based on an affine model of a spatialneighbor of the current block that is stored in a local buffer.
 15. Themethod of claim 1, further comprising: constructing a merge candidatelist or an AMVP candidate list, of which a maximum number of inheritedaffine candidates is more than two.
 16. The method of claim 15, whereinin response to a determination that the current block is adjacent to atop or the left boundary of the current CTU but not adjacent to atop-left corner of the current CTU, the merge candidate list or the AMVPcandidate list includes up to M1 inherited affine candidates from ahistory-based motion vector prediction (HMVP) table, M1 being an integergreater than or equal to 2, and up to N1 inherited affine candidatesdetermined based on regular motion information of minimum sized blocksalong the top or left boundary of the current CTU, N1 being an integergreater than or equal to 1, and in response to a determination that thecurrent block is adjacent to the top-left corner of the current CTU, themerge candidate list or the AMVP candidate list includes up to M2inherited affine candidates from the HMVP table, M2 being an integergreater than or equal to 1, up to K inherited affine candidatesdetermined based on regular motion information of minimum sized blocksalong the top boundary of the current CTU, K being an integer greaterthan or equal to 1, and up to N2 inherited affine candidates determinedbased on regular motion information of minimum sized blocks along theleft boundary of the current CTU, N2 being an integer greater than orequal to
 1. 17. The method of claim 1, further comprising: constructinga merge candidate list or an AMVP candidate list including an inheritedaffine candidate from a history-based motion vector prediction (HMVP)table that includes an HMVP candidate representing an affine model withaffine parameters.
 18. An apparatus of video decoding, comprising:processing circuitry configured to: receive a current block that isaffine coded and included in a current coding tree unit (CTU); inresponse to a determination that the current block is adjacent to atop-left corner, a left boundary, or a top boundary of the current CTU,check an availability of affine coded blocks that are outside thecurrent CTU and neighbor the current block at predefined candidatepositions according to a predefined order, determine an affine modelbased on regular motion information of minimum sized blockscorresponding to first N available affine coded blocks determined fromthe check of the availability of the affine coded blocks, N being aninteger greater than zero; and determine an inherited affine candidatebased on the determined affine model.
 19. The apparatus of claim 18,wherein the determination of the inherited affine candidate furtherincludes the processing circuitry being configured to: determine controlpoint motion vectors (CPMVs) of the current block based on thedetermined affine model; and determine the inherited affine candidatebased on the determined CPMVs.
 20. A non-transitory computer-readablemedium storing instructions that when executed by a computer for videodecoding cause the computer to perform a method for video decoding, themethod comprising: receiving a current block that is affine coded andincluded in a current coding tree unit (CTU); in response to adetermination that the current block is adjacent to a top-left corner, aleft boundary, or a top boundary of the current CTU, checking anavailability of affine coded blocks that are outside the current CTU andneighbor the current block at predefined candidate positions accordingto a predefined order; determining an affine model based on regularmotion information of minimum sized blocks corresponding to first Navailable affine coded blocks determined from the checking, N being aninteger greater than zero; and determining an inherited affine candidatebased on the determined affine model.